Light-emitting device and method for manufacturing the same

ABSTRACT

An object is to improve reliability of a light-emitting device. A light-emitting device has a driver circuit portion including a transistor for a driver circuit and a pixel portion including a transistor for a pixel over one substrate. The transistor for the driver circuit and the transistor for the pixel are inverted staggered transistors each including an oxide semiconductor layer in contact with part of an oxide insulating layer. In the pixel portion, a color filter layer and a light-emitting element are provided over the oxide insulating layer. In the transistor for the driver circuit, a conductive layer overlapping with a gate electrode layer and the oxide semiconductor layer is provided over the oxide insulating layer. The gate electrode layer, a source electrode layer, and a drain electrode layer are formed using metal conductive films.

TECHNICAL FIELD

The present invention relates to a light-emitting device including alayer containing an organic compound as a light-emitting layer, and amanufacturing method of the light-emitting device. For example, thepresent invention relates to an electronic device on which alight-emitting display device having an organic light-emitting elementis mounted as a part.

Note that in this specification, a semiconductor device refers to alldevices that can function by utilizing semiconductor characteristics,and electro-optic devices such as light-emitting devices, semiconductorcircuits, and electronic devices are all semiconductor devices.

BACKGROUND ART

A light-emitting element containing an organic compound as a luminousbody, which has features such as thinness, lightness, high-speedresponse, and DC drive at a low voltage, is expected to be applied to anext-generation flat panel display or a next-generation lighting device.In particular, a display device in which light-emitting elements arearranged in matrix is considered to have advantages in a wide viewingangle and excellent visibility over a conventional liquid crystaldisplay device.

It is said that, as for a light-emitting mechanism of a light-emittingelement, an EL layer is interposed between a pair of electrodes andvoltage is applied to the pair of electrodes, so that electrons injectedfrom a cathode and holes injected from an anode are recombined in anemission center of the EL layer to form molecular excitons, and themolecular excitons release energy when returning to a ground state,whereby light is emitted. Singlet excitation and triplet excitation areknown as excited states, and light emission can probably be achievedthrough either of the excited states.

An EL layer included in a light-emitting element includes at least alight-emitting layer. In addition, the EL layer can have a stacked-layerstructure including a hole-injection layer, a hole-transport layer, anelectron-transport layer, an electron-injection layer, and/or the like,in addition to the light-emitting layer.

As a material having semiconductor characteristics, metal oxide hasattracted attention. The examples of such metal oxides havingsemiconductor characteristics are tungsten oxide, tin oxide, indiumoxide, zinc oxide, and the like. A thin film transistor in which achannel formation region is formed using such metal oxide havingsemiconductor characteristics is known (for example, see PatentDocuments 1 and 2).

A TFT applying an oxide semiconductor has high field effect mobility.Therefore, a driver circuit in a display device or the like can beformed using the TFT.

REFERENCE

-   [Patent Document 1] Japanese Published Patent Application No.    2007-123861-   [Patent Document 2] Japanese Published Patent Application No.    2007-096055

DISCLOSURE OF INVENTION

For a thin film transistor including an oxide semiconductor film,high-speed operation, a relatively easy manufacturing process, andsufficient reliability are required.

An object is to improve operation characteristics and reliability of athin film transistor including an oxide semiconductor film.

In particular, higher operation speed of a thin film transistor used ina driver circuit is preferable.

For example, the operation speed is increased when a channel length (L)of the thin film transistor is reduced or a channel width (W) thereof isincreased. However, when the channel length is reduced, there is aproblem in that a switching characteristic, for example, an on-off ratiois lowered. In addition, when the channel width (W) is increased, thereis a problem in that the capacity load of the thin film transistoritself is increased.

Another object is to provide a light-emitting device including a thinfilm transistor having stable electric characteristics even when achannel length is small.

When a plurality of circuits which are different from each other isformed over an insulating surface, for example, when a pixel portion anda driver circuit are formed over one substrate, excellent switchingcharacteristics such as a high on-off ratio is needed for a thin filmtransistor used in the pixel portion, while high operation speed isneeded for a thin film transistor used in the driver circuit. Inparticular, as the definition of a display device is higher, writingtime of a displayed image is reduced. Therefore, it is preferable thatthe thin film transistor used for the driver circuit operate at highspeed.

Further, another object is to reduce variation in electricalcharacteristics of a thin film transistor including an oxidesemiconductor film.

One embodiment of the present invention is a light-emitting devicehaving a driver circuit portion including a transistor for a drivercircuit and a pixel portion including a transistor for a pixel over onesubstrate. Each of the transistor for the driver circuit and thetransistor for the pixel includes a gate electrode layer, a gateinsulating layer over the gate electrode layer, an oxide semiconductorlayer over the gate insulating layer, a source electrode layer and adrain electrode layer over the oxide semiconductor layer, and an oxideinsulating layer, which is in contact with part of the oxidesemiconductor layer, over the oxide semiconductor layer, the sourceelectrode layer, and the drain electrode layer. The pixel portion isprovided with a color filter layer over the oxide insulating layer and astack of a first electrode layer electrically connected to thetransistor for the pixel, an EL layer, and a second electrode layer overthe color filter layer. The transistor for the driver circuit isprovided with a conductive layer over the oxide insulating layer, whichoverlaps with the gate electrode layer and the oxide semiconductorlayer. The gate electrode layers, the source electrode layers, and thedrain electrode layers are formed using metal conductive films.

Another embodiment of the present invention is a light-emitting devicehaving a driver circuit portion including a transistor for a drivercircuit and a pixel portion including a transistor for a pixel over onesubstrate. Each of the transistor for the driver circuit and thetransistor for the pixel includes a gate electrode layer, a gateinsulating layer over the gate electrode layer, an oxide semiconductorlayer over the gate insulating layer, a source electrode layer and adrain electrode layer over the oxide semiconductor layer, and an oxideinsulating layer, which is in contact with part of the oxidesemiconductor layer, over the oxide semiconductor layer, the sourceelectrode layer, and the drain electrode layer. The pixel portion isprovided with a color filter layer over the oxide insulating layer and astack of a first electrode layer electrically connected to thetransistor for the pixel through a connection electrode layer, an ELlayer, and a second electrode layer over the color filter layer. Thetransistor for the driver circuit is provided with a conductive layerover the oxide insulating layer, which overlaps with the gate electrodelayer and the oxide semiconductor layer. The gate electrode layers, thesource electrode layers, and the drain electrode layers are formed usingmetal conductive films.

An inverted staggered transistor having a bottom-gate structure is usedas each of the transistor for the pixel and the transistor for the drivecircuit. The transistor for the pixel and the transistor for the drivercircuit are each a channel-etched transistor in which an oxideinsulating film is provided in contact with an oxide semiconductor layerwhich is exposed between a source electrode layer and a drain electrodelayer.

The transistor for the driver circuit has a structure in which the oxidesemiconductor layer is sandwiched between the gate electrode and theconductive layer. With this structure, variation in the thresholdvoltage of the transistor can be reduced; accordingly, a light-emittingdevice including a transistor with stable electric characteristics canbe provided. The conductive layer may have the same potential as thegate electrode layer or may have a floating potential or a fixedpotential such as GND potential or 0V. By setting the potential of theconductive layer to an appropriate value, the threshold voltage of thetransistor can be controlled.

The transistor for the pixel may be formed in direct contact with apixel electrode or may be electrically connected to the pixel electrodethrough the connection electrode layer. The connection electrode layermay be formed using a film including an element selected from Al, Cr,Cu, Ta, Ti, Mo, and W as its main component or a stacked film of alloyfilms containing any of the elements.

The conductive layer provided over the oxide semiconductor layer of thetransistor for the driver circuit, a first wiring (also referred to as aterminal or a connection electrode), and a second wiring (also referredto as a terminal or a connection electrode) may be formed using an oxideconductive material such as indium oxide, an alloy of indium oxide andtin oxide, an alloy of indium oxide and zinc oxide, or zinc oxide in thesame step as the pixel electrode or may be formed using a metal filmsuch as a film including an element selected from Al, Cr, Cu, Ta, Ti,Mo, and W as its main component or an alloy including any of theelements in the same step as the connection electrode layer.

Light-emitting elements emitting light with a plurality of colors andtransistors for pixels, which are electrically connected to thelight-emitting elements, may be formed over one substrate, so that alight-emitting device such as a display can be manufactured.

A plurality of light-emitting elements emitting white light may beprovided and an optical film, specifically color filters may be providedso as to overlap light-emitting regions of the light-emitting elements,so that a light-emitting display device capable of full-color displaycan be manufactured. Note that in this specification, the color filterrefers not to a whole of a film including color filter layers with threecolors (e.g., a red color filter, a blue color filter, and a green colorfilter) in addition to a black matrix and/or an overcoat but to a colorfilter with one color.

In order to realize the above structure, one embodiment of the presentinvention is a method for manufacturing a light-emitting device,including the steps of forming a gate electrode layer using a metalconductive film over a substrate having an insulating surface includingregions for a driver circuit portion and a pixel portion, forming a gateinsulating layer over the gate electrode layer, forming an oxidesemiconductor layer over the gate insulating layer, dehydrating ordehydrogenating the oxide semiconductor layer, without exposure to theair while water and hydrogen are prevented from entering the oxidesemiconductor layer again, forming a source electrode layer and a drainelectrode layer using a metal conductive film over the oxidesemiconductor layer, forming an oxide insulating layer, which is incontact with part of the oxide semiconductor layer, over the oxidesemiconductor layer, the source electrode layer, and the drain electrodelayer, whereby a transistor for a driver circuit is formed in the drivercircuit portion and a transistor for a pixel is formed in the pixelportion, forming a color filter layer over the oxide insulating layer inthe pixel portion, forming a first electrode layer over the color filterlayer, which is electrically connected to the transistor for the pixel,stacking an EL layer and a second electrode layer in this order over thefirst electrode layer, and forming a conductive layer over the oxideinsulating layer in the driver circuit portion, which overlaps with thegate electrode layer and the oxide semiconductor layer of the transistorfor the driver circuit, in the same step as the first electrode layer.

In order to realize the above structure, another embodiment of thepresent invention is a method for manufacturing a light-emitting device,including the steps of forming a gate electrode layer using a metalconductive film over a substrate having an insulating surface includingregions for a driver circuit portion and a pixel portion, forming a gateinsulating layer over the gate electrode layer, forming an oxidesemiconductor layer over the gate insulating layer, dehydrating ordehydrogenating the oxide semiconductor layer, without exposure to theair while water and hydrogen are prevented from entering the oxidesemiconductor layer again, forming a source electrode layer and a drainelectrode layer using a metal conductive film over the oxidesemiconductor layer, forming an oxide insulating layer, which is incontact with part of the oxide semiconductor layer, over the oxidesemiconductor layer, the source electrode layer, and the drain electrodelayer, whereby a transistor for a driver circuit is formed in the drivercircuit portion and a transistor for a pixel is formed in the pixelportion, forming a color filter layer over the oxide insulating layer inthe pixel portion, forming a first electrode layer over the color filterlayer, which is electrically connected to the transistor for the pixelthrough a connection electrode layer, stacking an EL layer and a secondelectrode layer in this order over the first electrode layer, andforming a conductive layer over the oxide insulating layer in the drivercircuit portion, which overlaps with the gate electrode layer and theoxide semiconductor layer of the transistor for the driver circuit, inthe same step as the connection electrode layer.

Note that in a photolithography step of the steps of manufacturing alight-emitting device, an etching step may be performed using a masklayer formed using a multi-tone mask which is a light-exposure maskthrough which light is transmitted so as to have a plurality ofintensities.

Since a mask layer formed with the use of a multi-tone mask has aplurality of film thicknesses and can be changed shapes thereof byperforming etching on the mask layer, the mask layer can be used in aplurality of etching steps for processing into different patterns.Therefore, a mask layer corresponding at least two kinds or more ofdifferent patterns can be formed by one multi-tone mask. Thus, thenumber of light-exposure masks can be reduced and the number ofcorresponding photolithography steps can also be reduced, wherebysimplification of a process can be realized.

With the above structure, at least one of the above problems can beresolved.

Oxide semiconductor used in this specification is formed into a thinfilm of a material expressed by InMO₃(ZnO)_(m) (m>0), and a thin filmtransistor in which the thin film is used as an oxide semiconductorlayer is manufactured. Note that M denotes one metal element or aplurality of metal elements selected from Ga, Fe, Ni, Mn, and Co. As anexample, M may be Ga or may include the above metal element in additionto Ga, for example, M may be Ga and Ni or Ga and Fe. Moreover, in theabove oxide semiconductor, in some cases, a transition metal elementsuch as Fe or Ni or an oxide of the transition metal is contained as animpurity element in addition to a metal element contained as M. In thisspecification, an oxide semiconductor layer whose composition formula isrepresented by InMO₃ (ZnO)_(m) (m>0) where at least Ga is included as Mis referred to as an In—Ga—Zn—O-based oxide semiconductor, and a thinfilm thereof is referred to as an In—Ga—Zn—O-based non-single-crystalfilm.

As the metal oxide applied to the oxide semiconductor layer, any of thefollowing metal oxide can be applied besides the above: anIn—Sn—Zn—O-based metal oxide; an In—Al—Zn—O-based metal oxide; aSn—Ga—Zn—O-based metal oxide; an Al—Ga—Zn—O-based metal oxide; aSn—Al—Zn—O-based metal oxide; an In—Zn—O-based metal oxide; aSn—Zn—O-based metal oxide; an Al—Zn—O-based metal oxide; an In—O-basedmetal oxide; a Sn—O-based metal oxide; and a Zn—O-based metal oxide.Alternatively, silicon oxide may be included in the oxide semiconductorlayer formed using the above metal oxide.

It can be said that, by heat treatment in an atmosphere of an inert gassuch as nitrogen or a rare gas (e.g., argon or helium), the oxidesemiconductor layer is changed into an oxygen-deficient oxidesemiconductor layer to have lower resistance, i.e., become an N-type(N⁻-type) oxide semiconductor layer and that then, by formation of anoxide insulating film in contact with the oxide semiconductor layer andheat treatment after the formation, the oxide semiconductor layer isplaced in an oxygen-excess state to have higher resistance, i.e., becomean i-type oxide semiconductor layer. In addition, it can also be saidthat solid phase oxidation by which the oxide semiconductor layer isplaced in an oxygen-excess state is performed. Thus, it is possible tomanufacture and provide a light-emitting device including a highlyreliable thin film transistor with favorable electrical characteristics.

As dehydration or dehydrogenation, heat treatment is performed in anatmosphere of an inert gas such as nitrogen or a rare gas (e.g., argonor helium) at a temperature higher than or equal to 400° C. and lowerthan or equal to 750° C., preferably higher than or equal to 425° C. andlower than or equal to 750° C., so that impurities such as moistureincluded in the oxide semiconductor layers are reduced. Further, water(H₂O) can be prevented from being contained again in the oxidesemiconductor layer later.

The heat treatment for dehydration or dehydrogenation is preferablyperformed in a nitrogen atmosphere with an H₂O concentration of 20 ppmor lower. Alternatively, the heat treatment may be performed inultra-dry air with an H₂O concentration of 20 ppm or lower.

The oxide semiconductor layer is subjected to heat treatment fordehydration or dehydrogenation under a condition that two peaks of wateror at least one peak of water at around 300° C. is not detected even ifTDS is performed at up to 450° C. on the oxide semiconductor layersubjected to dehydration or dehydrogenation. Therefore, even when a thinfilm transistor using the dehydrated or dehydrogenated oxidesemiconductor layer is subjected to TDS at a temperature as high as 450°C., at least a peak of water at around 300° C. is not detected.

In addition, it is important not to mix water or hydrogen into the oxidesemiconductor layer, without exposure to the air, with the use of thesame furnace in which dehydration or dehydrogenation is performed on theoxide semiconductor layer when the temperature is lowered from a heattemperature T at which dehydration or dehydrogenation is performed. Whena thin film transistor is formed using an oxide semiconductor layerobtained by changing an oxide semiconductor layer into a low-resistanceoxide semiconductor layer, i.e., an N-type (e.g., N⁻-type) oxidesemiconductor layer by dehydration or dehydrogenation and then bychanging the low-resistance oxide semiconductor layer into ahigh-resistance oxide semiconductor layer so as to be an i-typesemiconductor layer, the threshold voltage (V_(th)) of the thin filmtransistor can be positive voltage, so that a so-called normally-offswitching element can be realized. It is preferable for a semiconductordevice (display device) that a channel be formed with positive thresholdvoltage and as close to 0 V as possible in a thin film transistor. Notethat if the threshold voltage of the thin film transistor is negative,the thin film transistor tends to be normally on; in other words,current flows between a source electrode and a drain electrode even whengate voltage is 0 V. In an active matrix display device, the electricalcharacteristics of a thin film transistor included in a circuit areimportant and influence the performance of the display device. Among theelectrical characteristics of the thin film transistor, the thresholdvoltage is particularly important. When the threshold voltage is high ornegative even when field-effect mobility is high, it is difficult tocontrol the circuit. In the case where a thin film transistor has highthreshold voltage and a large absolute value of its threshold voltage,the thin film transistor cannot perform a switching function as the TFTand might be a load when the TFT is driven at low voltage. In the caseof an n-channel thin film transistor, it is preferable that a channel beformed and drain current flows after positive voltage is applied as gatevoltage. A transistor in which a channel is not formed unless drivingvoltage is increased and a transistor in which a channel is formed anddrain current flows even when negative voltage is applied are unsuitablefor a thin film transistor used in a circuit.

A gas atmosphere in which the heat temperature T is decreased may beswitched to a gas atmosphere different from that in which thetemperature is increased to the heat temperature T. For example, coolingis performed with the furnace used for dehydration or dehydrogenation,which is filled with a high-purity oxygen gas, a high-purity N₂O gas, orultra-dry air (having a dew point of −40 C. or lower, preferably −60° C.or lower), without exposure to the air.

The electrical characteristics of a thin film transistor are improvedusing an oxide semiconductor film cooled slowly (or cooled) in anatmosphere which does not contain moisture (having a dew point of −40°C. or lower, preferably −60° C. or lower) after moisture which iscontained in a film is reduced by heat treatment for dehydration ordehydrogenation, and high-performance thin film transistors which can bemass-produced are realized.

In this specification, heat treatment in the atmosphere of an inert gassuch as nitrogen or a rare gas (e.g., argon or helium) is referred to asheat treatment for dehydration or dehydrogenation. In thisspecification, for convenience, dehydration or dehydrogenation refersnot only to elimination of H₂ but also to elimination of H, OH, or thelike.

In the case where heat treatment is performed in an atmosphere of aninert gas such as nitrogen or a rare gas (e.g., argon or helium), anoxide semiconductor layer is changed into an oxygen-deficient oxidesemiconductor layer by the heat treatment to be a low-resistance oxidesemiconductor layer, i.e., an N-type (e.g., N⁻-type) oxide semiconductorlayer.

A region overlapping with the drain electrode layer is formed as ahigh-resistance drain region (also referred to as an HRD region) whichis an oxygen-deficient region. In addition, a region overlapping withthe source electrode layer is formed as a high-resistance source region(also referred to as an HRS region) which is an oxygen-deficient region.

In particular, the carrier concentration of the high-resistance drainregion is higher than or equal to 1×10¹⁸/cm³ and is at least higher thanthe carrier concentration of a channel formation region (lower than1×10¹⁸/cm³). Note that the carrier concentration in this specificationis carrier concentration obtained by Hall effect measurement at roomtemperature.

Then, a channel formation region is formed by making at least part ofthe dehydrated or dehydrogenated oxide semiconductor layer be in anoxygen-excess state so as to be a high-resistance oxide semiconductorlayer, i.e., an i-type oxide semiconductor layer. Note that as thetreatment for making part of dehydrated or dehydrogenated the oxidesemiconductor layer be in an oxygen-excess state, any of the followingmethods is employed; deposition of an oxide insulating film bysputtering over and in contact with the dehydrated or dehydrogenatedoxide semiconductor layer; heat treatment of the oxide insulating filmformed over and in contact with the dehydrated or dehydrogenated oxidesemiconductor layer; heat treatment of the oxide insulating film formedover and in contact with the dehydrated or dehydrogenated oxidesemiconductor layer in an atmosphere including oxygen; heat treatment ofthe oxide insulating film formed over and in contact with the dehydratedor dehydrogenated oxide semiconductor layer in an inert gas atmosphere,which is followed by cooling treatment in an oxygen atmosphere; and heattreatment of the oxide insulating film formed over and in contact withthe dehydrated or dehydrogenated oxide semiconductor layer in an inertgas atmosphere, which is followed by cooling treatment in ultra-dry air(having a dew point of −40° C. or lower, preferably −60° C. or lower).

Further, in order to use at least a part of the oxide semiconductorlayer subjected to dehydration or dehydrogenation (a portion overlappingwith a gate electrode layer) as the channel formation region, the oxidesemiconductor layer can be selectively made in an oxygen-excess state soas to be a high-resistance oxide semiconductor layer, i.e., an i-typeoxide semiconductor layer. The channel formation region can be formed insuch a manner that a source electrode layer and a drain electrode layerformed using metal electrodes of Ti or the like are formed on and incontact with the oxide semiconductor layer subjected to dehydration ordehydrogenation and exposure regions which do not overlap with thesource electrode layer and the drain electrode layer are selectivelymade to be in an oxygen-excess state. In the case where the exposureregions are selectively made to be in an oxygen-excess state, a firsthigh-resistance source region overlapping with the source electrodelayer and a second high-resistance drain region overlapping with thedrain electrode layer are formed, and the channel formation region isformed between the first high-resistance source region and the secondhigh-resistance drain region. That is, the channel formation region isformed between the source electrode layer and the drain electrode layerin a self-aligned manner.

Thus, it is possible to manufacture and provide a light-emitting deviceincluding a highly reliable thin film transistor with favorableelectrical characteristics.

Note that by forming the high-resistance drain region in the oxidesemiconductor layer overlapping with the drain electrode layer,reliability can be improved when a drive circuit is formed.Specifically, by forming the high-resistance drain regions, a structurecan be obtained in which conductivity can be varied stepwise from thedrain electrode layer to the high-resistance drain region and thechannel formation region. Therefore, in the case where the thin filmtransistor operates using the drain electrode layer connected to awiring for supplying a high power supply potential VDD, thehigh-resistance drain region serves as a buffer and a high electricfield is not applied locally even if the high electric field is appliedbetween the gate electrode layer and the drain electrode layer, so thatthe withstand voltage of the thin film transistor can be improved.

In addition, the high-resistance drain region and the high-resistancesource region are formed in the oxide semiconductor layers overlappingwith the drain electrode layer and the source electrode layer, so thatreduction in leakage current can be achieved in the channel formationregion in forming the driver circuit. In particular, by forming thehigh-resistance drain region, leakage current between the drainelectrode layer and the source electrode layer of the transistor flowsthrough the drain electrode layer, the high-resistance drain region onthe drain electrode layer side, the channel formation region, thehigh-resistance source region on the source electrode layer side, andthe source electrode layer in this order. In this case, in the channelformation region, leakage current flowing from the high-resistance drainregion on the drain electrode layer side to the channel formation regioncan be concentrated on the vicinity of an interface between the channelformation region and a gate insulating layer which has high resistancewhen the transistor is off Thus, the amount of leakage current in a backchannel portion (part of a surface of the channel formation region whichis apart from the gate electrode layer) can be reduced.

Further, the high-resistance source region overlapping with the sourceelectrode layer and the high-resistance drain region overlapping withthe drain electrode layer overlap with each other with part of the gateelectrode layer and the gate insulating layer therebetween depending onthe width of the gate electrode layer, and the intensity of an electricfield in the vicinity of an end portion of the drain electrode layer canbe reduced more effectively.

Further, an oxide conductive layer may be formed between the oxidesemiconductor layer and the source and drain electrodes. The oxideconductive layer preferably contains zinc oxide as a component andpreferably does not contain indium oxide. For example, zinc oxide, zincaluminum oxide, zinc aluminum oxynitride, gallium zinc oxide, or thelike can be used. The oxide conductive layer also functions as alow-resistance drain (LRD, also referred to as an LRN (low-resistancen-type conductivity)) region. In particular, the carrier concentrationof the low-resistance drain region is higher than that of thehigh-resistance drain region (HRD region), and preferably in the rangeof 1×10²⁰/cm³ to 1×10²¹/cm³ inclusive. The oxide conductive layer isprovided between the oxide semiconductor layer and the source and drainelectrodes, whereby contact resistance can be reduced and higher speedoperation of the transistor can be realized. Accordingly, frequencycharacteristics of a peripheral circuit (a driver circuit) can beimproved.

The oxide conductive layer and the metal layer for forming the sourceand drain electrodes can be formed in succession.

Further, the above-described first wiring and the second wiring may beformed using a wiring that is formed by stacking a metal material andthe same material as that of the oxide conductive layer functioning asthe LRN region or the LRD region. By stacking the metal and the oxideconductive layer, coverage at the step such as an overlapping portion ofwirings or an opening can be improved; thus, wiring resistance can belowered. Furthermore, effects of preventing local increase in resistanceof a wiring due to migration or the like and preventing disconnection ofa wiring can be expected; accordingly, a highly reliable light-emittingdevice can be provided.

Regarding the above-described connection between the first wiring andthe second wiring, when the oxide conductive layer is sandwichedtherebetween, it is expected to prevent increase in contact resistancewhich is caused by formation of an insulating oxide on a metal surfacein the connection portion (contact portion); accordingly, a highlyreliable light-emitting device can be provided.

Since a thin film transistor is easily broken due to static electricityor the like, a protective circuit for protecting the thin filmtransistor in the pixel portion is preferably provided over the samesubstrate for a gate line or a source line. The protective circuit ispreferably formed with a non-linear element including an oxidesemiconductor layer.

Note that the ordinal numbers such as “first” and “second” in thisspecification are used for convenience and do not denote the order ofsteps and the stacking order of layers. In addition, the ordinal numbersin this specification do not denote particular names which specify thepresent invention.

A light-emitting device, which is a semiconductor device, provided witha thin film transistor which includes an oxide semiconductor layer andhas excellent electric characteristics and high reliability can berealized.

BRIEF DESCRIPTION OF DRAWINGS

In the accompanying drawings:

FIG. 1 illustrates a light-emitting device;

FIGS. 2A to 2C illustrate a method for manufacturing a light-emittingdevice;

FIGS. 3A to 3C illustrate a method for manufacturing a light-emittingdevice;

FIGS. 4A and 4B illustrate a method for manufacturing a light-emittingdevice;

FIGS. 5A and 5B illustrate a method for manufacturing a light-emittingdevice;

FIGS. 6A to 6D illustrate a method for manufacturing a light-emittingdevice;

FIGS. 7A and 7B illustrate a method for manufacturing a light-emittingdevice;

FIGS. 8A to 8D illustrate a method for manufacturing a light-emittingdevice;

FIGS. 9A and 9B illustrate a method for manufacturing a light-emittingdevice;

FIG. 10 illustrates a light-emitting device;

FIGS. 11A1 to 11B2 illustrate a light-emitting device;

FIGS. 12A and 12B each illustrate a block diagram of a light-emittingdevice;

FIGS. 13A and 13B illustrate a structure and a timing chart of a signalline driver circuit;

FIGS. 14A to 14C illustrate circuit diagrams of a configuration of ashift register;

FIGS. 15A and 15B illustrate a circuit diagram and a timing chart of ashift register;

FIG. 16 illustrates a light-emitting device;

FIGS. 17A to 17D illustrate a method for manufacturing a light-emittingdevice;

FIGS. 18A and 18B illustrate a method for manufacturing a light-emittingdevice;

FIG. 19 illustrates an equivalent circuit diagram of a pixel of alight-emitting device;

FIGS. 20A to 20C each illustrate a light-emitting device;

FIGS. 21A and 21B each illustrate a light-emitting element;

FIGS. 22A and 22B illustrate a light-emitting device;

FIGS. 23A and 23B illustrate electronic devices;

FIGS. 24A and 24B illustrate electronic devices;

FIG. 25 illustrates an electronic device; and

FIG. 26 illustrates electronic devices.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described with reference tothe accompanying drawings. Note that the present invention is notlimited to the following description, and various changes for the modesand details thereof will be apparent to those skilled in the art unlesssuch changes depart from the spirit and the scope of the invention.Therefore, the present invention should not be interpreted as beinglimited to the following description of the embodiments. In thestructures to be given below, the same portions or portions havingsimilar functions are denoted by the same reference numerals indifferent drawings, and explanation thereof will not be repeated.

(Embodiment 1)

A light-emitting device including a thin film transistor and amanufacturing process thereof will be described with reference to FIG.1, FIGS. 2A to 2C, FIGS. 3A to 3C, FIGS. 4A and 4B, FIGS. 5A and 5B, andFIGS. 11A1 to 11B2.

FIG. 1 illustrates a light-emitting device which is one mode of thepresent invention. The light-emitting device in FIG. 1 is provided, overa substrate 100, with a pixel portion including a light-emittingelement, a thin film transistor 170, and a capacitor 147, and a drivercircuit portion including a thin film transistor 180. Further, a firstterminal 121, a connection electrode 120, and a terminal electrode 128for connection are provided in a terminal portion for a gate wiring anda second terminal 122 and a terminal electrode 129 for connection areprovided in a terminal portion of a source wiring. Moreover, an oxideinsulating film 107 and a protective insulating layer 106 are formedover the thin film transistor 180 and the thin film transistor 170.

The light-emitting element is formed using a stack including a firstelectrode layer 110, an EL layer 194, and a second electrode layer 195.A drain electrode layer of the thin film transistor 170 and the firstelectrode layer 110 are formed so as to be in contact with each other,so that the light-emitting element and the thin film transistor 170 areelectrically connected to each other. In the pixel portion, a colorfilter layer 191 is formed over the protective insulating layer 106. Thecolor filter layer 191 is covered with an overcoat layer 192, and theprotective insulating layer 109 is further formed thereover. The firstelectrode layer 110 is formed over the protective insulating layer 109.Further, a partition 193 separating between light-emitting elements isformed over the thin film transistor 170.

In the thin film transistor 180 of the driver circuit portion, aconductive layer 111 is provided over a gate electrode layer and asemiconductor layer and a drain electrode layer 165 b is electricallyconnected to a conductive layer 162 which is formed in the same step asthe gate electrode layer.

A manufacturing method will be described in detail with reference toFIGS. 2A to 2C, FIGS. 3A to 3C, FIGS. 4A and 4B, FIGS. 5A and 5B, andFIGS. 11A1 to 11B2. FIGS. 2A to 2C, FIGS. 3A to 3C, FIGS. 4A and 4B, andFIGS. 5A and 5B each correspond to a cross-sectional view of thelight-emitting device.

A conductive layer is formed over the entire surface of substrate 100having an insulating surface, and then a first photolithography step isperformed to form a resist mask. Then, unnecessary portions of theconductive layer are removed by etching, so that wirings and electrodes(a gate electrode layer 101, a gate electrode layer 161, the conductivelayer 162, a capacitor wiring layer 108, and the first terminal 121) areformed. Etching is preferably performed so that end portions of thewirings and electrodes have tapered shapes as illustrated in FIG. 2A,because coverage with a film stacked thereover can be improved. Notethat the gate electrode layer 101 and the gate electrode layer 161 areincluded in the gate wirings.

Although there is no particular limitation on a light-transmittingsubstrate which can be used as the substrate 100 having an insulatingsurface, the light-transmitting substrate needs to have heat resistancehigh enough to withstand at least heat treatment to be performed later.A glass substrate can be used as the substrate 100 having an insulatingsurface.

In the case where a glass substrate is used and the temperature at whichthe heat treatment to be performed later is high, a glass substratewhose strain point is greater than or equal to 730° C. is preferablyused. As a glass substrate, a glass material such as aluminosilicateglass, aluminoborosilicate glass, or barium borosilicate glass is used,for example. Note that in the case where a larger amount of barium oxide(BaO) than boric acid is contained, a glass substrate is heat-resistantand of more practical use. Therefore, a glass substrate containing BaOand B₂O₃ so that the amount of BaO is larger than that of B₂O₃ ispreferably used.

Note that a substrate formed using an insulator, such as a ceramicsubstrate, a quartz substrate, or a sapphire substrate, may be usedinstead of the above glass substrate. Alternatively, crystallized glassor the like may be used. Since the light-emitting device described inthis embodiment has a bottom-emission structure in which light isemitted through the surface on the substrate 100 side, alight-transmitting substrate is used as the substrate 100; however, inthe case where the light-emitting device has a top-emission structure inwhich light is emitted through the surface opposite to the substrate 100side, a non-light-transmitting substrate such as a metal substrate maybe used as the substrate 100.

An insulating film serving as a base film may be provided between thesubstrate 100, and the gate electrode layer 101, the gate electrodelayer 161, the conductive layer 162, the capacitor wiring layer 108, andthe first terminal 121. The base film has a function of preventingdiffusion of an impurity element from the substrate 100, and can beformed as a single-layer structure or a layered structure using one ormore of a silicon nitride film, a silicon oxide film, a silicon nitrideoxide film, and a silicon oxynitride film.

The gate electrode layer 101, the gate electrode layer 161, theconductive layer 162, the capacitor wiring layer 108, and the firstterminal 121 can be formed with a single layer or a stacked layer usinga metal material such as molybdenum, titanium, chromium, tantalum,tungsten, aluminum, copper, neodymium, or scandium, or an alloy materialwhich contains any of these materials as a main component.

For example, as a two-layer structure of each of the gate electrodelayer 101, the gate electrode layer 161, the conductive layer 162, thecapacitor wiring layer 108, and the first terminal 121, the followingstructures are preferable: a two-layer structure of an aluminum layerand a molybdenum layer stacked thereover, a two-layer structure of acopper layer and a molybdenum layer stacked thereover, a two-layerstructure of a copper layer and a titanium nitride layer or a tantalumnitride layer stacked thereover, and a two-layer structure of a titaniumnitride layer and a molybdenum layer. As a stacked structure of threelayers, a stacked layer of a tungsten layer or a tungsten nitride layer,an alloy of aluminum and silicon or an alloy of aluminum and titanium,and a titanium nitride layer or a titanium layer is preferable.

Next, a gate insulating layer 102 is formed over the gate electrodelayer 101, the gate electrode layer 161, the conductive layer 162, thecapacitor wiring layer 108, and the first terminal 121 (see FIG. 2A).

The gate insulating layer 102 can be formed to have a single layer of asilicon oxide layer, a silicon nitride layer, a silicon oxynitridelayer, a silicon nitride oxide layer, or an aluminum oxide layer or astacked layer thereof by a plasma CVD method, a sputtering method, orthe like. For example, a silicon oxynitride layer may be formed usingSiH₄, oxygen, and nitrogen as a film formation gas by a plasma CVDmethod. The thickness of the gate insulating layer 102 is set to greaterthan or equal to 100 nm and less than or equal to 500 nm. In the case ofa stacked structure, for example, a first gate insulating layer having athickness from 50 nm to 200 nm inclusive and a second gate insulatinglayer having a thickness from 5 nm to 300 nm inclusive are stacked inthis order.

In this embodiment, a silicon nitride layer having a thickness of 200 nmor less is formed by a plasma CVD method as the gate insulating layer102.

Then, an oxide semiconductor film 130 with a thickness of greater thanor equal to 2 nm and less than or equal to 200 nm is formed over thegate insulating layer 102 (see FIG. 2B).

Note that before the oxide semiconductor film is formed by a sputteringmethod, dust on a surface of the gate insulating layer 102 is preferablyremoved by reverse sputtering in which an argon gas is introduced andplasma is generated. The reverse sputtering is a method in which voltageis applied to a substrate side with the use of an RF power supply in anargon atmosphere and plasma is generated in the vicinity of thesubstrate so that a substrate surface is modified. Note that instead ofan argon atmosphere, a nitrogen atmosphere, a helium atmosphere, or thelike may be used. Alternatively, an argon atmosphere to which oxygen,N₂O, or the like is added may be used. Further alternatively, an argonatmosphere to which Cl₂, CF₄, or the like is added may be used.

The oxide semiconductor film 130 preferably has a thickness as small as50 nm or less so as to be amorphous even when the heat treatment fordehydration or dehydrogenation follows the formation of the oxidesemiconductor film 130. Reduction in thickness can prevent the oxidesemiconductor film from being crystallized when heat treatment isperformed after the formation of the oxide semiconductor layer.

The oxide semiconductor film 130 is formed using an In—Ga—Zn—O-basednon-single-crystal film, an In—Sn—Zn—O-based oxide semiconductor film,an In—Al—Zn—O-based oxide semiconductor film, a Sn—Ga—Zn—O-based oxidesemiconductor film, an Al—Ga—Zn—O-based oxide semiconductor film, aSn—Al—Zn—O-based oxide semiconductor film, an In—Zn—O-based oxidesemiconductor film, an Sn—Zn—O-based oxide semiconductor film, anAl—Zn—O-based oxide semiconductor film, an In—O-based oxidesemiconductor film, a Sn—O-based oxide semiconductor film, or aZn—O-based oxide semiconductor film. In this embodiment, the oxidesemiconductor film 130 is formed by a sputtering method with the use ofan In—Ga—Zn—O-based oxide semiconductor target. Alternatively, the oxidesemiconductor film 130 can be formed by a sputtering method under a raregas (typically argon) atmosphere, an oxygen atmosphere, or an atmosphereof a rare gas (typically argon) and oxygen. When a sputtering method isemployed, it is preferable that deposition be performed using a targetcontaining SiO₂ of 2 wt % to 10 wt % and SiOx (x>0) which inhibitscrystallization be contained in the oxide semiconductor film 130 so asto prevent crystallization at the time of the heat treatment fordehydration or dehydrogenation in a later step.

Here, the oxide semiconductor film is formed using an oxidesemiconductor target containing In, Ga, and Zn (In₂O₃:Ga₂O₃:ZnO=1:1:1[mol %], In:Ga:Zn=1:1:0.5 [at %]) under conditions where the distancebetween the substrate and the target is 100 mm, the pressure is 0.2 Pa,and the direct current (DC) power supply is 0.5 kW in an atmospherecontaining argon and oxygen (argon:oxygen=30 sccm:20 sccm, theproportion of the oxygen flow is 40%). Note that a pulse direct current(DC) power supply is preferable because dust can be reduced and the filmthickness can be uniform. The In—Ga—Zn—O-based non-single-crystal filmis formed to have a thickness of 5 nm to 200 nm inclusive. In thisembodiment, as the oxide semiconductor film, an In—Ga—Zn—O-basednon-single-crystal film having a thickness of 20 nm is formed using theIn—Ga—Zn—O-based oxide semiconductor target by a sputtering method.

Examples of a sputtering method include an RF sputtering method in whicha high-frequency power source is used as a sputtering power source, a DCsputtering method, and a pulsed DC sputtering method in which a bias isapplied in a pulsed manner. An RF sputtering method is mainly used inthe case of forming an insulating film, and a DC sputtering method ismainly used in the case of forming a metal film.

In addition, there is a multi-source sputtering apparatus in which aplurality of targets of different materials can be set. With themulti-source sputtering apparatus, films of different materials can bedeposited to be stacked in the same chamber, and a film of plural kindsof materials can be deposited by electric discharge at the same time inthe same chamber.

In addition, there are a sputtering apparatus provided with a magnetsystem inside the chamber and used for a magnetron sputtering, and asputtering apparatus used for an ECR sputtering in which plasmagenerated with the use of microwaves is used without using glowdischarge.

Furthermore, as a deposition method by sputtering, there are also areactive sputtering method in which a target substance and a sputteringgas component are chemically reacted with each other during depositionto form a thin compound film thereof, and a bias sputtering method inwhich a voltage is also applied to a substrate during deposition.

Next, a second photolithography step is performed. A resist mask 137 isformed over the oxide semiconductor film 130, and unnecessary portionsof the oxide semiconductor film 130 and the gate insulating layer 102are removed by etching to form a contact hole 119 reaching the firstterminal 121 and a contact hole 118 reaching the conductive layer 162 inthe gate insulating layer 102 (see FIG. 2C).

Thus, when the contact holes are formed in the gate insulating layer 102while the oxide semiconductor film 130 is formed over the entire surfaceof the gate insulating layer 102, the resist mask is not in directcontact with the surface of the gate insulating layer 102; accordingly,contamination of the surface of the gate insulating layer 102 (e.g.,attachment of impurities or the like to the gate insulating layer 102)can be prevented. Thus, a favorable state of the interface between thegate insulating layer 102 and the oxide semiconductor film 130 can beobtained, leading to improvement in reliability.

Alternatively, a resist pattern may be formed directly on the gateinsulating layer, and then contact holes may be formed. In such a case,heat treatment is preferably performed to dehydrate, dehydrogenate, ordehydroxylate the surface of the gate insulating film after removal ofthe resist. For example, impurities such as hydrogen and water includedin the gate insulating layer may be removed by heat treatment (at higherthan or equal to 400° C. and less than or equal to 750° C.) under aninert gas (e.g., nitrogen, helium, neon, or argon) atmosphere or anoxygen atmosphere.

Next, the resist mask 137 is removed. The oxide semiconductor film 130is etched with the use of resist masks 135 a and 135 b formed in a thirdphotolithography step, so that island-shaped oxide semiconductor layers131 and 132 are formed (see FIG. 3A). Alternatively, the resist masks135 a and 135 b used for forming the island-shaped oxide semiconductorlayers may be formed by an ink-jet method. When the resist masks areformed by an ink-jet method, the photomask is not used, leading toreduction in manufacturing cost.

Next, the oxide semiconductor layers 131 and 132 are subjected todehydration or dehydrogenation, so that dehydrated or dehydrogenatedoxide semiconductor layers 133 and 134 are formed (see FIG. 3B). Thetemperature of first heat treatment at which dehydration ordehydrogenation is performed is higher than or equal to 400° C. andlower than or equal to 750° C., preferably higher than or equal to 425°C. and lower than or equal to 750° C. Note that in the case where thetemperature of the first heat treatment is 425° C. or higher, the heattreatment time may be one hour or less, while in the case where thetemperature of the first heat treatment is lower than 425° C., the heattreatment time is set to more than one hour. Here, the substrate isintroduced into an electric furnace which is one example of heattreatment apparatuses, and the oxide semiconductor layers are subjectedto heat treatment in a nitrogen atmosphere. Then, the oxidesemiconductor layers are not exposed to air and water and hydrogen areprevented from entering the oxide semiconductor layers again. In thismanner, the oxide semiconductor layers 133 and 134 are formed. In thisembodiment, slow cooling is performed from the heating temperature T atwhich the oxide semiconductor layers are dehydrated or dehydrogenated toa temperature low enough to prevent entry of water again, specificallyto a temperature that is lower than the heating temperature T by 100° C.or more, in a nitrogen atmosphere in one furnace. Without limitation toa nitrogen atmosphere, dehydration or dehydrogenation may be performedin a rare gas atmosphere such as helium, neon, or argon.

When the oxide semiconductor layers are subjected to heat treatment at400° C. to 700° C., the dehydration or dehydrogenation of the oxidesemiconductor layers can be achieved; thus, water (H₂O) can be preventedfrom being contained again in the oxide semiconductor layers in latersteps.

The heat treatment apparatus is not limited to the electric furnace,and, for example, may be an RTA (rapid thermal annealing) apparatus suchas a GRTA (gas rapid thermal annealing) apparatus or an LRTA (lamp rapidthermal annealing) apparatus. An LRTA apparatus is an apparatus forheating an object to be processed by radiation of light (anelectromagnetic wave) emitted from a lamp such as a halogen lamp, ametal halide lamp, a xenon arc lamp, a carbon arc lamp, a high-pressuresodium lamp, or a high-pressure mercury lamp. In addition, the LRTAapparatus may be provided with not only a lamp but also a device whichheats an object to be processed by heat conduction or heat radiationfrom a heater such as a resistance heater. GRTA is a method of heattreatment using a high-temperature gas. As the gas, an inert gas whichdoes not react with an object to be processed by heat treatment, forexample, nitrogen or a rare gas such as argon, is used. The heattreatment may be performed by an RTA method at 600° C. to 750° C. forseveral minutes.

Note that in the first heat treatment, it is preferable that water,hydrogen and the like be not contained in nitrogen, or the rare gas suchas helium, neon, or argon. In particular, the heat treatment which isperformed on the oxide semiconductor layers for dehydration ordehydrogenation at 400° C. to 750° C. is preferably performed in anitrogen atmosphere in which the concentration of H₂O is 20 ppm orlower. Alternatively, it is preferable that nitrogen or a rare gas suchas helium, neon, or argon introduced into an apparatus for heattreatment have purity of 6N (99.9999%) or more, preferably, 7N(99.99999%) or more; that is, an impurity concentration is set to 1 ppmor lower, preferably, 0.1 ppm or lower.

In some cases, the oxide semiconductor layers are crystallized to bemicrocrystalline films or polycrystalline films depending on theconditions of the first heat treatment or the material of the oxidesemiconductor layers. For example, the oxide semiconductor layers maycrystallize to become microcrystalline semiconductor layers having adegree of crystallization of 90% or more, or 80% or more. Further,depending on the conditions of the first heat treatment and the materialof the oxide semiconductor layers, the oxide semiconductor layers maybecome amorphous oxide semiconductor layers containing no crystallinecomponent.

The first heat treatment of the oxide semiconductor layer can also beperformed on the oxide semiconductor film 130 which has not beenprocessed into the island-shaped oxide semiconductor layers 131 and 132.In that case, after the first heat treatment, the substrate is taken outof the heating device and a photolithography step is performed.

The heat treatment for dehydration or dehydrogenation of the oxidesemiconductor layers may be performed at any of the following timings:after the oxide semiconductor layers are formed; after a sourceelectrode and a drain electrode are formed over the oxide semiconductorlayer; and after a passivation film is formed over the source electrodeand the drain electrode.

Further, the step of forming the contact holes 118 and 119 in the gateinsulating layer 102 as illustrated in FIG. 2C may be performed afterthe oxide semiconductor film 130 is subjected to dehydration ordehydrogenation treatment.

Note that this etching step of the oxide semiconductor film is notlimited to wet etching and dry etching may also be performed.

As the etching gas for dry etching, a gas containing chlorine(chlorine-based gas such as chlorine (Cl₂), boron chloride (BCl₃),silicon chloride (SiCl₄), or carbon tetrachloride (CCl₄)) is preferablyused.

Alternatively, a gas containing fluorine (fluorine-based gas such ascarbon tetrafluoride (CF₄), sulfur fluoride (SF₆), nitrogen fluoride(NF₃), or trifluoromethane (CHF₃)); hydrogen bromide (HBr); oxygen (O₂);any of these gases to which a rare gas such as helium (He) or argon (Ar)is added; or the like can be used.

As the dry etching method, a parallel plate RIE (reactive ion etching)method or an ICP (inductively coupled plasma) etching method can beused. In order to etch the films into desired shapes, the etchingcondition (the amount of electric power applied to a coil-shapedelectrode, the amount of electric power applied to an electrode on asubstrate side, the temperature of the electrode on the substrate side,or the like) is adjusted as appropriate.

As an etchant used for wet etching, a solution obtained by mixingphosphoric acid, acetic acid, and nitric acid, an ammonia peroxidemixture (hydrogen peroxide: ammonia:water=5:2:2), or the like can beused. In addition, ITO07N (produced by KANTO CHEMICAL CO., INC.) mayalso be used.

The etchant used in the wet etching is removed by cleaning together withthe material which is etched off. The waste liquid including the etchantand the material etched off may be purified and the material may bereused. When a material such as indium included in the oxidesemiconductor layer is collected from the waste liquid after the etchingand reused, the resources can be efficiently used and the cost can bereduced.

The etching conditions (such as an etchant, etching time, andtemperature) are adjusted as appropriate depending on the material sothat the material can be etched into a desired shape.

Next, a metal conductive film is formed using a metal material over theoxide semiconductor layers 133 and 134 by a sputtering method or avacuum evaporation method.

As a material of the metal conductive film, there are an elementselected from Al, Cr, Cu, Ta, Ti, Mo, or W, an alloy including the aboveelement, an alloy film in which some of the above elements are combined,and the like. Further, the metal conductive film may have a single-layerstructure or a stacked-layer structure of two or more layers. Forexample, a single-layer structure of an aluminum film including silicon,a two-layer structure in which a titanium film is stacked over analuminum film, a three-layer structure in which a Ti film, an aluminumfilm, and a Ti film are stacked in this order, and the like can begiven. Alternatively, a film, an alloy film, or a nitride film whichcontains Al and one or a plurality of elements selected from titanium(Ti), tantalum (Ta), tungsten (W), molybdenum (Mo), chromium (Cr),neodymium (Nd), and scandium (Sc) may be used.

In the case where heat treatment is performed after formation of themetal conductive film, the metal conductive film preferably has heatresistance enough to withstand the heat treatment.

Next, a fourth photolithography step is performed. Resist masks 136 a,136 b, 136 c, 136 d, 136 e, 136 f, and 136 g are formed, and unnecessaryportions of the metal conductive film are removed by etching, so that asource electrode layer 105 a, a drain electrode layer 105 b, a sourceelectrode layer 165 a, the drain electrode layer 165 b, a capacitorelectrode layer 149, the connection electrode 120, and the secondterminal 122 are formed (see FIG. 3C).

Note that each material and etching conditions are adjusted asappropriate so that the oxide semiconductor layers 133 and 134 are notremoved by etching of the metal conductive film.

In this embodiment, a Ti film is used as the metal conductive film, anIn—Ga—Zn—O-based oxide semiconductor film is used as the oxidesemiconductor layers 133 and 134, and an ammonia hydrogen peroxidesolution (a mixture of ammonia, water, and a hydrogen peroxide solution)is used as an etchant.

In the fourth photolithography step, the connection electrode 120 andthe second terminal 122, which are formed using the same material asthat of the source electrode layers 105 a and 165 a and the drainelectrode layers 105 b and 165 b, are formed in the respective terminalportions. Note that the second terminal 122 is electrically connected toa source wiring (a source wiring including the source electrode layers105 a and 165 a). The connection electrode 120 is formed in contact withthe first terminal 121 in the contact hole 119 and electricallyconnected to the first terminal 121.

Note that the resist masks 136 a, 136 b, 136 c, 136 d, 136 e, 136 f, and136 g used for forming the source electrode layers and the drainelectrode layers may be formed by an ink-jet method. When the resistmask is formed by an ink-jet method, the photomask is unnecessary;accordingly, the manufacturing cost can be reduced.

Next, the resist masks 136 a, 136 b, 136 c, 136 d, 136 e, 136 f, and 136g are removed, and an oxide insulating film 107 serving as a protectiveinsulating film in contact with the oxide semiconductor layers 133 and134 is formed.

At this stage, in the oxide semiconductor layers 133 and 134, there areregions in contact with the oxide insulating film. Among these regions,the regions which are in contact with the oxide insulating film 107 andoverlap with the gate electrode layers with the gate insulating layerinterposed therebetween are channel formation regions.

The oxide insulating film 107 can be formed to have a thickness of atleast 1 nm or more by a sputtering method or the like, as appropriate,which is a method with which impurities such as water and hydrogen arenot mixed into the oxide insulating film 107. In this embodiment, asilicon oxide film with a thickness of 300 nm is formed as the oxideinsulating film 107 by a sputtering method. The substrate temperature infilm formation may be greater than or equal to room temperature and lessthan or equal to 300° C. In this embodiment, the substrate temperatureis at room temperature. The silicon oxide film can be formed by asputtering method in a rare gas (typically argon) atmosphere, an oxygenatmosphere, or an atmosphere including a rare gas (typically argon) andoxygen. Further, a silicon oxide target or a silicon target can be usedas a target. For example, a silicon oxide film can be formed by asputtering method using a silicon target in an oxygen atmosphere. As theoxide insulating film which is formed in contact with the oxidesemiconductor layer whose resistance is reduced, an inorganic insulatingfilm which does not include impurities such as moisture, a hydrogen ion,and OH⁻ and blocks entry of these from the outside is used.Specifically, a silicon oxide film, a silicon nitride oxide film, analuminum oxide film, or an aluminum oxynitride film is used.

Next, second heat treatment is performed in an inert gas atmosphere or anitrogen atmosphere at a preferable temperature from 200° C. to 400° C.inclusive, e.g., from 250° C. to 350° C. inclusive. For example, thesecond heat treatment is performed in a nitrogen atmosphere at 250° C.for one hour. By the second heat treatment, part of the oxidesemiconductor layers 133 and 134 which overlaps with the oxideinsulating film 107 is heated in the state of being in contact with theoxide insulating film 107.

Through the above-described steps, heat treatment for dehydration ordehydrogenation is performed on the oxide semiconductor layer afterdeposition to reduce the resistance, and then, part of the oxidesemiconductor layer is selectively made to be in an oxygen-excess state.

As a result, in the oxide semiconductor layer 133, a channel formationregion 166 overlapping with the gate electrode layer 161 has i-typeconductivity, and a high-resistance source region 167 a overlapping withthe source electrode layer 165 a and a high-resistance drain region 167b overlapping with the drain electrode layer 165 b are formed in aself-aligned manner; thus, an oxide semiconductor layer 163 is formed.Similarly, in the oxide semiconductor layer 134, a channel formationregion 116 overlapping with the gate electrode layer 101 has i-typeconductivity, and a high-resistance source region 117 a overlapping withthe source electrode layer 105 a and a high-resistance drain region 117b overlapping with the drain electrode layer 105 b are formed in aself-aligned manner; thus, an oxide semiconductor layer 103 is formed.

By formation of the high-resistance drain regions 117 b and 167 b (orthe high-resistance source regions 117 a and 167 a) in the oxidesemiconductor layers 103 and 163 which overlap with the drain electrodelayers 105 b and 165 b (and the source electrode layers 105 a and 165a), respectively, reliability in a formed circuit can be improved.Specifically, by formation of the high-resistance drain region 117 b, astructure can be employed in which conductivity is varied stepwise fromthe drain electrode layer 105 b to the high-resistance drain region 117b and the channel formation region 116; similarly, by formation of thehigh-resistance drain region 167 b, a structure can be employed in whichconductivity is varied stepwise from the drain electrode layer 165 b tothe high-resistance drain region 167 b and the channel formation region166. Therefore, when the transistors operate in the state of beingconnected to a wiring which supplies the drain electrode layers 105 band 165 b with a high power source potential VDD, the high-resistancedrain regions serve as buffers so that a local high electric field isnot applied even when a high electric field is applied between the gateelectrode layer 101 and the drain electrode layer 105 b and between thegate electrode layer 161 and the drain electrode layer 165 b; in thismanner, the transistors each can have a structure with an increasedwithstand voltage.

In addition, by formation of the high-resistance drain regions 117 b and167 b (or the high-resistance source regions 117 a and 167 a) in theoxide semiconductor layers 103 and 163 which overlap with the drainelectrode layers 105 b and 165 b (and the source electrode layers 105 aand 165 a), respectively, leakage current in the channel formationregions 116 and 166 which may flow in a formed circuit can be reduced.

In this embodiment, after a silicon oxide film is formed by a sputteringmethod as the oxide insulating film 107, heat treatment is performed at250° C. to 350° C., whereby oxygen enters each of the oxidesemiconductor layers from the exposed portion (the channel formationregion) of the oxide semiconductor layer between the source region andthe drain region, and is diffused thereinto. By formation of the siliconoxide film by a sputtering method, an excessive amount of oxygen can becontained in the silicon oxide film, and oxygen can enter the oxidesemiconductor layers and can be diffused thereinto through the heattreatment. Oxygen enters the oxide semiconductor layers and is diffusedthereinto, whereby the channel region can have higher resistance (i.e.,the channel region can have i-type conductivity). Thus, the thin filmtransistors can serve as normally-off transistors.

Further, the high-resistance source region or the high-resistance drainregion in the oxide semiconductor layer is formed in the entirethickness direction in the case where the thickness of the oxidesemiconductor layer is 15 nm or smaller. In the case where the thicknessof the oxide semiconductor layer is 30 nm or larger and 50 nm orsmaller, in part of the oxide semiconductor layer, that is, in a regionin the oxide semiconductor layer which is in contact with the sourceelectrode layer or the drain electrode layer and the vicinity thereof,resistance is reduced and a high-resistance source region or ahigh-resistance drain region is formed, while a region in the oxidesemiconductor layer, which is close to the gate insulating film, can bemade to be an I type.

A protective insulating layer may be additionally formed over the oxideinsulating film 107. For example, a silicon nitride film is formed by anRF sputtering method. Since an RF sputtering method has highproductivity, it is preferably used as a deposition method of theprotective insulating layer. As the protective insulating layer, aninorganic insulating film which does not include impurities such asmoisture, a hydrogen ion, and OH⁻ and blocks entry of these from theoutside is used. Specifically, a silicon nitride film, an aluminumnitride film, a silicon nitride oxide film, an aluminum oxynitride film,or the like is used. In this embodiment, a silicon nitride film isformed as the protective insulating layer 106 (see FIG. 4A).

Through the above steps, the thin film transistor 170 in the pixelportion, the transistor 180 in the driver circuit portion, and thecapacitor 147 can be manufactured over the same substrate. Each of thethin film transistors 170 and 180 is a bottom-gate thin film transistorincluding an oxide semiconductor layer in which a high-resistance sourceregion, a high-resistance drain region, and a channel formation regionare formed. Therefore, in each of the thin film transistors 170 and 180,the high-resistance drain region or the high-resistance source regionserves as a buffer, so that a local high electric field is not appliedeven when a high electric field is applied; in this manner, the thinfilm transistors 170 and 180 can each have a structure with an increasedwithstand voltage.

The capacitor 147 is formed using the gate insulating layer 102, thecapacitor wiring layer 108, and the capacitor electrode layer 149, inwhich the gate insulating layer 102 in the capacitor portion is used asa dielectric.

By providing the driver circuit and the pixel portion over the samesubstrate, connection wirings between the driver circuit and an externalsignal can be shortened; thus, reduction in size and cost of thelight-emitting device can be achieved.

Then, the color filter layer 191 is formed over the protectiveinsulating layer 106. As the color filter layer, a green color filterlayer, a blue color filter layer, a red color filter layer, or the likecan be used, and a green color filter layer, a blue color filter, and ared color filter layer are sequentially formed. Each color filter layeris formed by a printing method, an ink-jet method, an etching methodwith the use of a photolithography technique, or the like. By providingthe color filter layers, alignment of the color filter layers andlight-emitting regions of light-emitting elements can be performedwithout depending on the attachment accuracy of the sealing substrate.In this embodiment, fifth, sixth, and seventh photolithography steps areperformed to form a green color filter layer, a blue color filter layer,and a red color filter layer.

Next, an overcoat layer 192 which covers the color filter layers (thegreen color filter layer, the blue color filter layer, and the red colorfilter layer) is formed. The overcoat layer 192 is formed using alight-transmitting resin. In this embodiment, the overcoat layer 192 isformed in an eighth photolithography step.

Here, an example in which full color display is performed using threecolors of RGB is shown; however, the invention is not particularlylimited thereto, and full color display may be performed using fourcolors of RGBW.

Next, a protective insulating layer 109 which covers the overcoat layer192 and the protective insulating layer 106 is formed (see FIG. 4B). Forthe protective insulating layer 109, an inorganic insulating film suchas a silicon nitride film, an aluminum nitride film, a silicon nitrideoxide film, or an aluminum oxynitride film is used. It is preferablethat the protective insulating layer 109 be an insulating film havingthe same component as that of the protective insulating layer 106because they can be etched in one step when a contact hole is formed.

Next, a ninth photolithography step is performed. A resist mask isformed, and a contact hole 125 which reaches the drain electrode layer105 b is formed by etching the oxide insulating film 107, the protectiveinsulating layer 106, and the protective insulating layer 109. Then, theresist mask is removed (see FIG. 5A). In addition, a contact hole 127which reaches the second terminal 122 and a contact hole 126 whichreaches the connection electrode 120 are also formed by this etching.Alternatively, a resist mask for forming the contact holes may be formedby an ink-jet method. A photomask is not used when the resist mask isformed by an ink-jet method, leading to reduction in manufacturing cost.

Next, a light-transmitting conductive film is formed. Thelight-transmitting conductive film is formed using a material such asindium oxide (In₂O₃) or an alloy of indium oxide and tin oxide(In₂O₃—SnO₂, abbreviated to ITO) by a sputtering method, a vacuumevaporation method, or the like. Alternatively, an Al—Zn—O-basednon-single-crystal film containing nitrogen (i.e., an Al—Zn—O—N-basednon-single-crystal film), a Zn—O-based non-single-crystal filmcontaining nitrogen, or a Sn—Zn—O-based non-single-crystal filmcontaining nitrogen may be used as the material of thelight-transmitting conductive film. Note that the composition ratio(atomic %) of zinc in the Al—Zn—O—N-based non-single-crystal film isless than or equal to 47 atomic % and is higher than that of aluminum inthe non-single-crystal film; the composition ratio (atomic %) ofaluminum in the Al—Zn—O—N-based non-single-crystal film is higher thanthat of nitrogen in the non-single-crystal film. Such a material isetched with a hydrochloric acid-based solution. However, since a residueis easily left on the substrate particularly in etching ITO, an alloy ofindium oxide and zinc oxide (In₂O₃—ZnO) may be used in order to improveetching processability.

Note that the unit of the composition ratio in the light-transmittingconductive film is atomic percent (atomic %), and the composition ratiois evaluated by analysis using an electron probe X-ray microanalyzer(EPMA).

Next, a tenth photolithography step is performed. A resist mask isformed, and unnecessary portions of the light-transmitting conductivefilm are removed by etching, so that the first electrode layer 110, theconductive layer 111, and the terminal electrodes 128 and 129 areformed. Then, the resist mask is removed.

The capacitor 147, which includes the gate insulating layer 102 as adielectric, the capacitor wiring layer 108, and the capacitor electrodelayer 149, can also be formed over the same substrate as the drivercircuit portion and the pixel portion. In a light-emitting device, thecapacitor electrode layer 149 is part of a power supply line, and thecapacitor wiring layer 108 is part of a gate electrode layer of a driverTFT.

The terminal electrodes 128 and 129 which are formed in the terminalportion function as electrodes or wirings connected to an FPC. Theterminal electrode 128 formed over the first terminal 121 with theconnection electrode 120 therebetween is a connection terminal electrodeserving as an input terminal for the gate wiring. The terminal electrode129 formed over the second terminal 122 is a connection terminalelectrode serving as an input terminal for the source wiring.

Further, FIGS. 11A1 and 11A2 are a cross-sectional view of a gate wiringterminal portion at this stage and a top view thereof, respectively.FIG. 11A1 is a cross-sectional view taken along line C1-C2 in FIG. 11A2.In FIG. 11A1, a conductive film 155 formed over the oxide insulatingfilm 107 is a connection terminal electrode serving as an inputterminal. Furthermore, in FIG. 11A1, in the terminal portion, a firstterminal 151 formed using the same material as that of the gate wiringand a connection electrode 153 formed using the same material as that ofthe source wiring overlap with each other with the gate insulating layer102 therebetween, and are electrically connected to each other. Inaddition, the connection electrode 153 and the conductive film 155 arein direct contact with each other through a contact hole provided in theoxide insulating film 107 to form conduction therebetween.

Further, FIGS. 11B1 and 11B2 are a cross-sectional view of a sourcewiring terminal portion at this stage and a top view thereof,respectively. FIG. 11B1 corresponds to a cross-sectional view takenalong line D1-D2 in FIG. 11B2. In FIG. 11B1, the conductive film 155formed over the oxide insulating film 107 is a connection terminalelectrode serving as an input terminal. Furthermore, in FIG. 11B1, inthe terminal portion, an electrode 156 formed using the same material asthat of the gate wiring is located below and overlapped with the secondterminal 150, which is electrically connected to the source wiring, withthe gate insulating layer 102 therebetween. The electrode 156 is notelectrically connected to the second terminal 150, and a capacitor forpreventing noise or static electricity can be formed when the potentialof the electrode 156 is set to a potential different from that of thesecond terminal 150, such as floating, GND, or 0 V. The second terminal150 is electrically connected to the conductive film 155 with the oxideinsulating film 107 therebetween.

A plurality of gate wirings, source wirings, and capacitor wirings areprovided depending on the pixel density. In the terminal portion, thefirst terminal at the same potential as the gate wiring, the secondterminal at the same potential as the source wiring, the third terminalat the same potential as the capacitor wiring, and the like are eacharranged in plurality. The number of each of the terminals may be anynumber, and the number of the terminals may be determined by apractitioner as appropriate.

The thin film transistors and the storage capacitor are arranged inmatrix in respective pixels so that a pixel portion is formed, which canbe used as one of substrates for manufacturing an active matrix displaydevice. In this specification, such a substrate is referred to as anactive matrix substrate for convenience.

The conductive layer 111 is provided so as to overlap with the channelformation region 166 in the oxide semiconductor layer, whereby in abias-temperature stress test (referred to as a BT test) for examiningthe reliability of a thin film transistor, the amount of change inthreshold voltage of the thin film transistor 180 before and after theBT test can be reduced. A potential of the conductive layer 111 may bethe same as or different from that of the gate electrode layer 161. Theconductive layer 111 can also serve as a second gate electrode layer.Alternatively, the potential of the conductive layer 111 may be GND or 0V, or the conductive layer 111 may be in a floating state.

Next, a partition 193 is formed so as to cover the periphery of thefirst electrode layer 110. The partition 193 is formed using a film ofan organic resin such as polyimide, acrylic, polyamide, or epoxy, aninorganic insulating film, or a siloxane-based resin.

Note that the siloxane-based resin corresponds to a resin including aSi—O—Si bond formed using a siloxane-based material as a startingmaterial. The siloxane-based resin may include, as a substituent, anorganic group (e.g., an alkyl group or an aryl group) or a fluoro group.In addition, the organic group may include a fluoro group.

The partition 193 can be formed using phosphosilicate glass (PSG),borophosphosilicate glass (BPSG), or the like. Note that the partition193 may be formed by stacking a plurality of insulating films formedusing any of these materials.

There is no particular limitation on the method for forming thepartition 193. The partition 193 can be formed, depending on thematerial, with a method such as a sputtering method, an SOG method, aspin coating method, a dipping method, a spray coating method, or adroplet discharge method (e.g., an ink-jet method, screen printing, oroffset printing), or with a means such as a doctor knife, a roll coater,a curtain coater, or a knife coater. Further, other insulating layersused in the light-emitting device may be formed using the materials andthe methods which are shown as examples of the materials and the methodsof the partition 193.

It is particularly preferable that the partition 193 be formed using aphotosensitive resin material to have an opening portion over the firstelectrode layer 110 so that a sidewall of the opening portion is formedas a tilted surface with continuous curvature. When the partition 193 isformed using a photosensitive resin material, a step for forming aresist mask can be omitted. In this embodiment, an eleventhphotolithography steps is performed, so that the partition 193 isformed.

The EL layer 194 is formed over the first electrode layer 110 and thesecond electrode layer 195 is formed over the EL layer 194, whereby alight-emitting element is formed. The second electrode layer 195 iselectrically connected to a common potential line. Any of a variety ofmaterials can be used for the second electrode layer 195. Specifically,the second electrode layer 195 is preferably formed using a materialhaving a low work function such as an alkali metal such as Li or Cs; analkaline earth metal such as Mg, Ca, or Sr; an alloy containing any ofthese metals (e.g., Mg:Ag or Al:Li); or a rare earth metal such as Yb orEr. In this embodiment, an aluminum film is used as the second electrodelayer 195.

Through these eleven photolithography steps with the use of the elevenphotomasks, the light-emitting device of this embodiment illustrated inFIG. 1 can be manufactured, which includes the driver circuit portionincluding the thin film transistor 180, the pixel portion including thethin film transistor 170 and the light-emitting element, the capacitor147 including the storage capacitor, and the external extractionterminal portions.

Further, in this embodiment, an example where the contact holes in theoxide insulating film 107, the protective insulating layer 106, and theprotective insulating layer 109 are formed in one photolithography stepis described; however, the contact holes may be formed in a plurality ofphotolithography steps with different photomasks. For example, the fifthphotolithography step may be performed to form the contact holes in theoxide insulating film 107 and the protective insulating layer 106serving as interlayer insulating layers, the sixth to ninthphotolithography steps may be performed to form the RGB color filterlayers and the overcoat layer, and then the contact holes may be formedin the protective insulating layer 109 in the tenth photolithographystep. In this case, the number of photolithography steps and photomasksincreases by one; accordingly, the light-emitting device is formedthrough the twelve photolithography steps with twelve photomasks.

Note that in the above-described photolithography steps, an etching stepmay be performed with the use of a mask layer formed using a multi-tonemask which is a light-exposure mask through which light is transmittedso as to have a plurality of intensities.

Since a mask layer formed with the use of a multi-tone mask has aplurality of film thicknesses and can be changed shapes thereof byperforming etching on the mask layer, the mask layer can be used in aplurality of etching steps for processing into different patterns.Therefore, a mask layer corresponding at least two kinds or more ofdifferent patterns can be formed by one multi-tone mask. Thus, thenumber of light-exposure masks can be reduced and the number ofcorresponding photolithography steps can also be reduced, wherebysimplification of a process can be realized.

Further, when a light-emitting device is manufactured, a power supplyline electrically connected to the source electrode layer of the driverTFT is provided. The power supply line intersects with a gate wiring anda source wiring and is formed using the same material and in the samestep as the gate electrode layer.

Further, in the case where a light-emitting device is manufactured, oneelectrode of the light-emitting element is electrically connected to thedrain electrode layer of the driver TFT, and a common potential linewhich is electrically connected to the other electrode of thelight-emitting element is provided. Note that the common potential linecan be formed using the same material and step as those of the gateelectrode layer.

Further, in the case where a light-emitting device is manufactured, aplurality of thin film transistors is provided in one pixel, and aconnection portion which connects the gate electrode layer of one thinfilm transistor to the drain electrode layer of the other thin filmtransistor is provided.

The use of an oxide semiconductor for a thin film transistor leads toreduction in manufacturing cost. In particular, an oxide insulating filmis formed in contact with an oxide semiconductor layer by the abovemethod, whereby a thin film transistor having stable electriccharacteristics can be manufactured and provided. Therefore, alight-emitting device which includes highly reliable thin filmtransistors having excellent electric characteristics can be provided.

The channel formation region in the semiconductor layer is ahigh-resistance region; thus, electric characteristics of the thin filmtransistor are stabilized and increase in off current or the like can beprevented. Therefore, a light-emitting device including a highlyreliable thin film transistor having favorable electric characteristicscan be provided.

Since a thin film transistor is easily broken due to static electricityor the like, a protective circuit is preferably provided over the samesubstrate as the pixel portion or the drive circuit. The protectivecircuit is preferably formed with a non-linear element including anoxide semiconductor layer. For example, protective circuits are providedbetween the pixel portion and a scan line input terminal and between thepixel portion and a signal line input terminal. In this embodiment, aplurality of protective circuits are provided so that the pixeltransistor and the like are not broken when surge voltage due to staticelectricity or the like is applied to a scan line, a signal line, and acapacitor bus line. Therefore, the protective circuit is formed so as torelease charge to a common wiring when surge voltage is applied to theprotective circuit. Further, the protective circuit includes non-linearelements arranged in parallel to each other with the scan linetherebetween. The non-linear element includes a two-terminal elementsuch as a diode or a three-terminal element such as a transistor. Forexample, the non-linear element can also be formed through the same stepas the thin film transistor 170 in the pixel portion, and can be made tohave the same properties as a diode by connecting a gate terminal to adrain terminal of the non-linear element.

This embodiment can be implemented in appropriate combination with thestructures described in the other embodiments.

(Embodiment 2)

In this embodiment, an example in which oxide conductive layers areprovided as a source region and a drain region between the oxidesemiconductor layer and the source and drain electrode layers inEmbodiment 1 will be described with reference to FIGS. 6A to 6D andFIGS. 7A and 7B. Therefore, part of this embodiment can be performed ina manner similar to that of Embodiment 1; thus, repetitive descriptionof the same portions as or portions having functions similar to those inEmbodiment 1 and steps for forming such portions will be omitted. SinceFIGS. 6A to 6D and FIGS. 7A and 7B are the same as FIG. 1, FIGS. 2A to2C, FIGS. 3A to 3C, FIGS. 4A and 4B, and FIGS. 5A and 5B except for partof steps, the same portions are denoted by the same reference numeralsand detailed description of the same portions is omitted.

First, the steps up to and including the step in FIG. 3B in Embodiment 1are performed in accordance with Embodiment 1. FIG. 6A illustrates thesame step as FIG. 3B.

An oxide conductive film 140 is formed over the dehydrated ordehydrogenated oxide semiconductor layers 133 and 134, and a metalconductive film formed using a metal conductive material is stacked overthe oxide conductive film 140.

As a deposition method of the oxide conductive film 140, a sputteringmethod, a vacuum evaporation method (e.g., an electron beam evaporationmethod), an arc discharge ion plating method, or a spray method is used.A material of the oxide conductive film 140 preferably contains zincoxide as a component and preferably does not contain indium oxide. Forsuch an oxide conductive film 140, zinc oxide, aluminum zinc oxide,aluminum zinc oxynitride, gallium zinc oxide, or the like can be used.The thickness of the oxide conductive film is selected as appropriate inthe range of 50 nm to 300 nm inclusive. In addition, in the case where asputtering method is used, it is preferable that deposition be performedusing a target containing SiO₂ at 2 wt % to 10 wt %, and SiO_(x) (x>0),which inhibits crystallization, be contained in the oxide conductivefilm so that crystallization is suppressed when the heat treatment fordehydration or dehydrogenation is performed in a later step.

Next, a fourth photolithography step is performed. The resist masks 136a, 136 b, 136 c, 136 d, 136 e, 136 f, and 136 g are formed, andunnecessary portions of the metal conductive film are removed byetching, so that the source electrode layer 105 a, the drain electrodelayer 105 b, the source electrode layer 165 a, the drain electrode layer165 b, the capacitor electrode layer 149, the connection electrode 120,and the second terminal 122 are formed (see FIG. 6B).

Note that each material and etching conditions are adjusted asappropriate so that the oxide conductive film 140 and the oxidesemiconductor layers 133 and 134 are not removed in etching of the metalconductive film.

Next, the resist masks 136 a, 136 b, 136 c, 136 d, 136 e, 136 f, and 136g are removed, and the oxide conductive film 140 is etched using thesource electrode layer 105 a, the drain electrode layer 105 b, thesource electrode layer 165 a, and the drain electrode layer 165 b asmasks, so that oxide conductive layers 164 a and 164 b, oxide conductivelayers 104 a and 104 b, and a capacitor electrode layer 185 are formed(see FIG. 6C). The oxide conductive film 140 containing zinc oxide as acomponent can be easily etched with an alkaline solution such as aresist stripping solution, for example. In addition, oxide conductivelayers 138 and 139 are also formed in respective terminal portions inthis step.

Etching treatment for dividing the oxide conductive layer to formchannel formation regions is performed by utilizing the difference inetching rates between the oxide semiconductor layers and the oxideconductive layer. The oxide conductive layer over the oxidesemiconductor layers is selectively etched utilizing a higher etchingrate of the oxide conductive film as compared to that of the oxidesemiconductor layers.

Therefore, removal of the resist masks 136 a, 136 b, 136 c, 136 d, 136e, 136 f, and 136 g is preferably performed by ashing. In the case ofetching with a stripping solution, etching conditions (the kind of theetchant, the concentration, and the etching time) are adjusted asappropriate so that the oxide conductive film 140 and the oxidesemiconductor layers 133 and 134 are not etched excessively.

As described in this embodiment, in the case where the island-shapedoxide semiconductor layers are formed by etching, the oxide conductivefilm and the metal conductive film are stacked thereover, and etching isperformed using the same masks to form a wiring pattern including sourceelectrode layers and drain electrode layers, oxide conductive films canbe left under the wiring pattern of the metal conductive film.

At the contact portion between the gate wiring (the conductive layer162) and the source wiring (the drain electrode layer 165 b), the oxideconductive layer 164 b is formed below the source wiring. The oxideconductive layer 164 b serves as a buffer, the resistance is only theseries resistance depending on the thickness of the oxide conductivelayer, and further the oxide conductive layer 164 b does not form aninsulating oxide with metal, which is preferable.

Next, the oxide insulating film 107 serving as a protective insulatingfilm is formed in contact with the oxide semiconductor layer 133 and134. In this embodiment, a silicon oxide film with a thickness of 300 nmis deposited as the oxide insulating film 107 by a sputtering method.

Next, second heat treatment is performed in an inert gas atmosphere or anitrogen atmosphere at a preferable temperature from 200° C. to 400° C.inclusive, e.g., from 250° C. to 350° C. inclusive. For example, thesecond heat treatment is performed in a nitrogen atmosphere at 250° C.for one hour. By the second heat treatment, part of the oxidesemiconductor layers 133 and 134 which overlaps with the oxideinsulating film 107 is heated in the state of being in contact with theoxide insulating film 107.

Through the above-described steps, heat treatment for dehydration ordehydrogenation is performed on the oxide semiconductor layer afterdeposition to reduce the resistance, and then, part of the oxidesemiconductor layer is selectively made to be in an oxygen-excess state.

As a result, in the oxide semiconductor layer 133, a channel formationregion 166 overlapping with the gate electrode layer 161 has i-typeconductivity, and a high-resistance source region 167 a overlapping withthe source electrode layer 165 a and the oxide conductive layer 164 aand a high-resistance drain region 167 b overlapping with the drainelectrode layer 165 b and the oxide conductive layer 164 b are formed ina self-aligned manner; thus, an oxide semiconductor layer 163 is formed.Similarly, in the oxide semiconductor layer 134, a channel formationregion 116 overlapping with the gate electrode layer 101 has i-typeconductivity, and a high-resistance source region 117 a overlapping withthe source electrode layer 105 a and the oxide conductive layer 104 aand a high-resistance drain region 117 b overlapping with the drainelectrode layer 105 b and the oxide conductive layer 164 b are formed ina self-aligned manner; thus, an oxide semiconductor layer 103 is formed.

The oxide conductive layers 104 b and 164 b which are disposed betweenthe oxide semiconductor layers 103 and 163 and the drain electrodelayers 105 b and 165 b formed using a metal material each also functionas a low-resistance drain (LRD, also referred to as an LRN(low-resistance n-type conductivity)) region. Similarly, the oxideconductive layers 104 a and 164 a which are disposed between the oxidesemiconductor layers 103 and 163 and the source electrode layers 105 aand 165 a formed using a metal material each also function as alow-resistance source (LRS, also referred to as an LRN (low-resistancen-type conductivity)) region. With the structure including the oxidesemiconductor layer, the low-resistance drain region, and the drainelectrode layer formed using a metal material, withstand voltage of thetransistor can be further increased. Specifically, the carrierconcentration of the low-resistance drain region is higher than that ofthe high-resistance drain region (the HRD region) and preferably in arange of 1×10²⁰/cm³ or higher and 1×10²⁰/cm³ or lower.

Through the above steps, a thin film transistor 171 in the pixel portionand a transistor 181 in the driver circuit portion can be manufacturedover the same substrate. Each of the thin film transistors 171 and 181is a bottom-gate thin film transistor including an oxide semiconductorlayer in which a high-resistance source region, a high-resistance drainregion, and a channel formation region are formed. Therefore, in each ofthe thin film transistors 171 and 181, the high-resistance drain regionor the high-resistance source region serves as a buffer, so that a localhigh electric field is not applied even when a high electric field isapplied; in this manner, the thin film transistors 171 and 181 can eachhave a structure with an increased withstand voltage.

In the capacitor portion, a capacitor 146 is formed from a stack of thecapacitor wiring layer 108, the gate insulating layer 102, the capacitorelectrode layer 185 formed in the same step as the oxide conductivelayer 104 b, and the capacitor electrode layer 149 formed in the samestep as the drain electrode layer 105 b.

Next, the protective insulating layer 106 is formed over the oxideinsulating film 107 and the color filter layer 191 is formed over theprotective insulating layer 106 in the pixel portion. The overcoat layer192 is formed so as to cover the color filter layer 191 and theprotective insulating layer 109 is formed so as to cover the protectiveinsulating layer 106 and the overcoat layer 192.

Next, a ninth photolithography step is performed in a similar manner inEmbodiment 1. A resist mask is formed, and the contact hole 125 whichreaches the drain electrode layer 105 b is formed by etching the oxideinsulating film 107, the protective insulating layer 106, and theprotective insulating layer 109. Then, the resist mask is removed (seeFIG. 6D). In addition, the contact hole 127 which reaches the secondterminal 122 and the contact hole 126 which reaches the connectionelectrode 120 are also formed by this etching.

Next, a light-transmitting conductive film is formed, and a tenthphotolithography step is performed. A resist mask is formed andunnecessary portions of the light-transmitting conductive film areremoved by etching to form the first electrode layer 110, the conductivelayer 111, and the terminal electrodes 128 and 129. Then, the resistmasks are removed (see FIG. 7A).

As in Embodiment 1, the partition 193 is formed in an eleventhphotolithography step. The EL layer 194 and the second electrode layer195 are stacked over the first electrode layer 110, so that thelight-emitting device of this embodiment which includes a light-emittingelement is manufactured (see FIG. 7B).

When the oxide conductive layers are provided between the oxidesemiconductor layer and the source and drain electrode layers as thesource region and the drain region, the source region and the drainregion can have lower resistance and the transistor can operate at highspeed. It is effective to use the oxide conductive layers for a sourceregion and a drain region in order to improve frequency characteristicsof a peripheral circuit (a driver circuit). This is because the contactbetween a metal electrode (e.g., Ti) and an oxide conductive layer canreduce the contact resistance as compared to the contact between a metalelectrode (e.g., Ti) and an oxide semiconductor layer.

There has been a problem in that molybdenum (Mo) which is used as a partof a wiring material (e.g., Mo/Al/Mo) in a light-emitting device hashigh contact resistance with an oxide semiconductor layer. This isbecause Mo is less likely to be oxidized and has a weaker effect ofextracting oxygen from the oxide semiconductor layer as compared to Ti,and a contact interface between Mo and the oxide semiconductor layer isnot changed to have an n-type conductivity. However, even in such acase, the contact resistance can be reduced by interposing an oxideconductive layer between the oxide semiconductor layer and source anddrain electrode layers; accordingly, frequency characteristics of aperipheral circuit (a driver circuit) can be improved.

The channel length of the thin film transistor is determined at the timeof etching the oxide conductive layer; accordingly, the channel lengthcan be further shortened. For example, the channel length L can be setas small as 0.1 μm to 2 μm inclusive; in this way, operation speed canbe increased.

This embodiment can be implemented in appropriate combination with thestructures described in the other embodiments.

(Embodiment 3)

In this embodiment, another example in which oxide conductive layers areprovided as a source region and a drain region between the oxidesemiconductor layer and the source and drain electrode layers inEmbodiment 1 or 2 will be described with reference to FIGS. 8A to 8D andFIGS. 9A and 9B. Therefore, part of this embodiment can be performed ina manner similar to that of Embodiment 1 or 2; thus, repetitivedescription of the same portions as or portions having functions similarto those in Embodiment 1 or 2 and steps for forming such portions willbe omitted. Since FIGS. 8A to 8D and FIGS. 9A and 9B are the same asFIG. 1, FIGS. 2A to 2C, FIGS. 3A to 3C, FIGS. 4A and 4B, FIGS. 5A and5B, FIGS. 6A to 6D, and FIGS. 7A and 7B except for part of steps, thesame portions are denoted by the same reference numerals and detaileddescription of the same portions is omitted.

First, in accordance with Embodiment 1, a metal conductive film isformed over the substrate 100, and the metal conductive film is etchedusing a resist mask formed in a first photolithography step, so that thefirst terminal 121, the gate electrode layer 161, the conductive layer162, the gate electrode layer 101, and the capacitor wiring layer 108are formed.

Next, the gate insulating layer 102 is formed over the first terminal121, the gate electrode layer 161, the conductive layer 162, the gateelectrode layer 101, and the capacitor wiring layer 108, and then anoxide semiconductor film and an oxide conductive film are stacked. Thegate insulating layer, the oxide semiconductor film, and the oxideconductive film can be formed in succession without being exposed toair.

Resist masks are formed over the oxide conductive film in a secondphotolithography step. The gate insulating layer, the oxidesemiconductor film, and the oxide conductive film are etched using theresist masks to form the contact hole 119 which reaches the firstterminal 121 and the contact hole 118 which reaches the conductive layer162.

The resist masks formed in the second photolithography step are removed,and resist masks are newly formed over the oxide conductive film in athird photolithography step. With the use of the resist masks in thethird photolithography step, island-shaped oxide semiconductor layersand island-shaped oxide conductive layers are formed.

When the contact holes are formed in the gate insulating layer in thestate where the oxide semiconductor film and the oxide conductive filmare stacked over the entire surface of the gate insulating layer in sucha manner, the resist masks are not directly in contact with the surfaceof the gate insulating layer; accordingly, contamination of the surfaceof the gate insulating layer (e.g., attachment of impurities or the liketo the gate insulating layer) can be prevented. Thus, a favorable stateof the interfaces between the gate insulating layer and the oxidesemiconductor film and between the gate insulating layer and the oxideconductive film can be obtained, whereby reliability can be improved.

Next, heat treatment for dehydration or dehydrogenation is performed inthe state where the oxide semiconductor layers and the oxide conductivelayers are stacked. By the heat treatment at 400° C. to 700° C., thedehydration or dehydrogenation of the oxide semiconductor layers can beachieved; thus, water (H₂O) can be prevented from being contained againin the oxide semiconductor layers in later steps.

As long as a substance which inhibits crystallization such as siliconoxide is not contained in the oxide conductive layers, the oxideconductive layers are crystallized through this heat treatment. Crystalof the oxide conductive layers grow in a columnar shape with respect toa base surface. Accordingly, when the metal conductive film formed overthe oxide conductive layers is etched in order to form a sourceelectrode layer and a drain electrode layer, formation of an undercutcan be prevented.

Further, by the heat treatment for dehydration or dehydrogenation of theoxide semiconductor layers, conductivity of the oxide conductive layerscan be improved. Note that only the oxide conductive layers may besubjected to heat treatment at a temperature lower than that for theoxide semiconductor layers.

The first heat treatment of the oxide semiconductor layers and the oxideconductive layers can also be performed on the oxide semiconductor filmand the oxide conductive film which have not been processed intoisland-shaped oxide semiconductor layers and the island-shaped oxideconductive layers. In that case, after the first heat treatment, thesubstrate is taken out of the heating device and a photolithography stepis performed.

Through the above-described steps, the oxide semiconductor layers 133and 134 and oxide conductive layers 142 and 143 can be obtained (seeFIG. 8A). The oxide semiconductor layer 133 and the oxide conductivelayer 142 are island-shaped stacked layers formed using the same mask,and the oxide semiconductor layer 134 and the oxide conductive layer 143are island-shaped stacked layers formed using the same mask.

Next, a fourth photolithography step is performed. The resist masks 136a, 136 b, 136 c, 136 d, 136 e, 136 f, and 136 g are formed, andunnecessary portions of the metal conductive film are removed byetching, so that the source electrode layer 105 a, the drain electrodelayer 105 b, the source electrode layer 165 a, the drain electrode layer165 b, the capacitor electrode layer 149, the connection electrode 120,and the second terminal 122 are formed (see FIG. 8B).

Note that each material and etching conditions are adjusted asappropriate so that the oxide conductive layers 142 and 143 and theoxide semiconductor layers 133 and 134 are not removed in etching of themetal conductive film.

Next, the resist masks 136 a, 136 b, 136 c, 136 d, 136 e, 136 f, and 136g are removed, and then the oxide conductive layers 142 and 143 areetched using the source electrode layer 105 a, the drain electrode layer105 b, the source electrode layer 165 a, and the drain electrode layer165 b as masks, so that the oxide conductive layers 164 a and 164 b andthe oxide conductive layers 104 a and 104 b are formed (see FIG. 8C).The oxide conductive layers 142 and 143 containing zinc oxide as acomponent can be easily etched with an alkaline solution such as aresist stripping solution, for example.

Therefore, removal of the resist masks 136 a, 136 b, 136 c, 136 d, 136e, 136 f, and 136 g is preferably performed by ashing. In the case ofetching with a stripping solution, etching conditions (the kind of theetchant, the concentration, and the etching time) are adjusted asappropriate so that the oxide conductive layers 142 and 143 and theoxide semiconductor layers 133 and 134 are not etched excessively.

Next, the oxide insulating film 107 serving as a protective insulatingfilm is formed in contact with the oxide semiconductor layer 133 and134. In this embodiment, a silicon oxide film with a thickness of 300 nmis deposited as the oxide insulating film 107 by a sputtering method.

Next, second heat treatment is performed in an inert gas atmosphere or anitrogen atmosphere at a preferable temperature from 200° C. to 400° C.inclusive, e.g., from 250° C. to 350° C. inclusive. For example, thesecond heat treatment is performed in a nitrogen atmosphere at 250° C.for one hour. By the second heat treatment, part of the oxidesemiconductor layers 133 and 134 which overlaps with the oxideinsulating film 107 is heated in the state of being in contact with theoxide insulating film 107.

Through the above-described steps, heat treatment for dehydration ordehydrogenation is performed on the oxide semiconductor layer afterdeposition to reduce the resistance, and then, part of the oxidesemiconductor layer is selectively made to be in an oxygen-excess state.

As a result, in the oxide semiconductor layer 133, a channel formationregion 166 overlapping with the gate electrode layer 161 has i-typeconductivity, and a high-resistance source region 167 a overlapping withthe source electrode layer 165 a and the oxide conductive layer 164 aand a high-resistance drain region 167 b overlapping with the drainelectrode layer 165 b and the oxide conductive layer 164 b are formed ina self-aligned manner; thus, an oxide semiconductor layer 163 is formed.Similarly, in the oxide semiconductor layer 134, a channel formationregion 116 overlapping with the gate electrode layer 101 has i-typeconductivity, and a high-resistance source region 117 a overlapping withthe source electrode layer 105 a and the oxide conductive layer 104 aand a high-resistance drain region 117 b overlapping with the drainelectrode layer 105 b and the oxide conductive layer 164 b are formed ina self-aligned manner; thus, an oxide semiconductor layer 103 is formed.

The oxide conductive layers 104 b and 164 b which are disposed betweenthe oxide semiconductor layers 103 and 163 and the drain electrodelayers 105 b and 165 b formed using a metal material each also functionas a low-resistance drain (LRD, also referred to as an LRN) region.Similarly, the oxide conductive layers 104 a and 164 a which aredisposed between the oxide semiconductor layers 103 and 163 and thesource electrode layers 105 a and 165 a formed using a metal materialeach also function as a low-resistance source (LRS, also referred to asan LRN) region. With the structure including the oxide semiconductorlayer, the low-resistance drain region, and the drain electrode layerformed using a metal material, withstand voltage of the transistor canbe further increased. Specifically, the carrier concentration of thelow-resistance drain region is higher than that of the high-resistancedrain region (the HRD region) and preferably in a range of 1×10²⁰/cm³ orhigher and 1×10²¹/cm³ or lower.

Through the above steps, a thin film transistor 172 in the pixel portionand a transistor 182 in the driver circuit portion can be manufacturedover the same substrate. Each of the thin film transistors 172 and 181is a bottom-gate thin film transistor including an oxide semiconductorlayer in which a high-resistance source region, a high-resistance drainregion, and a channel formation region are formed. Therefore, in each ofthe thin film transistors 172 and 181, the high-resistance drain regionor the high-resistance source region serves as a buffer, so that a localhigh electric field is not applied even when a high electric field isapplied; in this manner, the thin film transistors 172 and 182 can eachhave a structure with an increased withstand voltage.

In the capacitor portion, the capacitor 147 is formed from a stack ofthe capacitor wiring layer 108, the gate insulating layer 102, and thecapacitor electrode layer 149 formed in the same step as the drainelectrode layer 105 b.

Next, the protective insulating layer 106 is formed over the oxideinsulating film 107 and the color filter layer 191 is formed over theprotective insulating layer 106 in the pixel portion. The overcoat layer192 is formed so as to cover the color filter layer 191 and theprotective insulating layer 109 is formed so as to cover the protectiveinsulating layer 106 and the overcoat layer 192.

Next, a ninth photolithography step is performed in a similar manner inEmbodiment 1. A resist mask is formed, and the contact hole 125 whichreaches the drain electrode layer 105 b is formed by etching the oxideinsulating film 107, the protective insulating layer 106, and theprotective insulating layer 109. Then, the resist mask is removed (seeFIG. 8D). In addition, the contact hole 127 which reaches the secondterminal 122 and the contact hole 126 which reaches the connectionelectrode 120 are also formed by this etching.

Next, a light-transmitting conductive film is formed, and a tenthphotolithography step is performed. A resist mask is formed andunnecessary portions of the light-transmitting conductive film areremoved by etching to form the first electrode layer 110, the conductivelayer 111, and the terminal electrodes 128 and 129. Then, the resistmasks are removed (see FIG. 9A).

As in Embodiment 1, the partition 193 is formed in an eleventhphotolithography step. The EL layer 194 and the second electrode layer195 are stacked over the first electrode layer 110, so that thelight-emitting device of this embodiment which includes a light-emittingelement is manufactured (see FIG. 9B).

When the oxide conductive layers are provided between the oxidesemiconductor layer and the source and drain electrode layers as thesource region and the drain region, the source region and the drainregion can have lower resistance and the transistor can operate at highspeed. It is effective to use the oxide conductive layers for a sourceregion and a drain region in order to improve frequency characteristicsof a peripheral circuit (a driver circuit). This is because the contactbetween a metal electrode (e.g., Ti) and an oxide conductive layer canreduce the contact resistance as compared to the contact between a metalelectrode (e.g., Ti) and an oxide semiconductor layer.

The contact resistance can be reduced by interposing the oxideconductive layers between the oxide semiconductor layer and the sourceand drain electrode layers; accordingly, frequency characteristics of aperipheral circuit (a driver circuit) can be improved.

The channel length of the thin film transistor is determined at the timeof etching the oxide conductive layer; accordingly, the channel lengthcan be further shortened. For example, the channel length L can be setas small as 0.1 μm to 2 μm inclusive; in this way, operation speed canbe increased.

This embodiment can be implemented in appropriate combination with thestructures described in the other embodiments.

(Embodiment 4)

In this embodiment, an example of a light-emitting device in which athin film transistor in a pixel portion and a first electrode layer of alight-emitting element are electrically connected to each other througha connection electrode layer will be described with reference to FIG.16, FIGS. 17A to 17D, and FIGS. 18A and 18B. Note that in thisembodiment, materials and methods similar to those in Embodiment 1 canbe used except for a connection method of the transistor in the pixelportion and the first electrode layer of the light-emitting element.Therefore, part of this embodiment can be performed in a manner similarto that of Embodiment 1; thus, repetitive description of the sameportions as or portions having functions similar to those in Embodiment1 and steps for forming such portions will be omitted. Since FIG. 16,FIGS. 17A to 17D, and FIGS. 18A and 18B are the same as FIG. 1, FIGS. 2Ato 2C, FIGS. 3A to 3C, FIGS. 4A and 4B, and FIGS. 5A and 5B except forpart of steps, the same portions are denoted by the same referencenumerals and detailed description of the same portions is omitted.

A light-emitting device of this embodiment is illustrated in FIG. 16.The drain electrode layer 105 b of the thin film transistor 170 in thepixel portion is electrically connected to the first electrode layer 110through a connection electrode layer 196. A method for manufacturing thelight-emitting device illustrated in FIG. 16 will be described withreference to FIGS. 17A to 17D and FIGS. 18A and 18B.

First, according to Embodiment 1, the steps up to and including the stepin FIG. 4A in Embodiment 1 are performed. FIG. 17A illustrates the samestep as FIG. 4A.

Next, a fifth photolithography step is performed. A resist mask isformed, and the contact hole 125 which reaches the drain electrode layer105 b, the contact hole 127 which reaches the second terminal 122, andthe contact hole 126 which reaches the connection electrode 120 areformed by etching the oxide insulating film 107 and the protectiveinsulating layer 106. Then, the resist mask is removed (see FIG. 17B).

Next, a conductive film is formed, and a sixth photolithography step isperformed. Resist masks are formed and unnecessary portions of theconductive film are removed by etching to form the connection electrodelayer 196, a conductive layer 112, and terminal electrodes 113 and 114.Then, the resist masks are removed (see FIG. 17C). As the conductivefilm, a metal conductive film can be used; therefore, the connectionelectrode layer 196, the conductive layer 112, and the terminalelectrodes 113 and 114 can be formed of a metal conductive layer.

As the connection electrode layer 196, a film including an elementselected from Al, Cr, Cu, Ta, Ti, Mo, and W as its main component or astacked film including a film of any of the elements and an alloy filmthereof can be used. Accordingly, in the case where the conductive layer112 and the terminal electrodes 113 and 114 are formed in the same stepas the connection electrode layer 196 as in this embodiment, theconductive layer 112 and the terminal electrodes 113 and 114 can also beformed using a film including an element selected from Al, Cr, Cu, Ta,Ti, Mo, and W as its main component or a stacked film including a filmof any of the elements and an alloy film thereof. The conductive film isnot limited to a single layer including the above element and can beformed in a stacked layer of two or more layers. As a deposition methodof the conductive film, a sputtering method, a vacuum evaporation method(e.g., an electron beam evaporation method), an arc discharge ionplating method, or a spray method can be used.

Next, the RGB color filter layers 191 is formed over the protectiveinsulating layer 106 in the pixel portion in seventh to ninthphotolithography steps and the overcoat layer 192 is formed so as tocover the color filter layers 191 in a tenth photolithography step. Theprotective insulating layer 109 is formed so as to cover the connectionelectrode layer 196, the conductive layer 112, the terminal electrodes113 and 114, the protective insulating layer 106, and the overcoat layer192 (see FIG. 17D).

Next, an eleventh photolithography step is performed. A resist mask isformed, and the contact hole 125 which reaches the connection electrodelayer 196 is formed by etching the protective insulating layer 109.Then, the resist mask is removed. In addtion, the protective insulatinglayer 109 over the terminal electrodes 113 and 114 is also removed bythis etching, so that the terminal electrodes 113 and 114 are exposed(see FIG. 18A).

Then, a light-transmitting conductive film is formed. A twelfthphotolithography step is performed. A resist mask is formed andunnecessary portions of the light-transmitting conductive film areetched to form the first electrode layer 110. Then, the resist mask isremoved.

As in Embodiment 1, the partition 193 is formed in a thirteenthphotolithography step. The EL layer 194 and the second electrode layer195 are stacked over the first electrode layer 110 and thus thelight-emitting device of this embodiment, which includes alight-emitting element, is manufactured (see FIG. 18B).

In the case where the connection electrode layer 196 is formed, a powersupply line can be formed using the same material as and in the samestep as the connection electrode layer 196. Further, a common potentialline can also be formed using the same material as and in the same stepas the connection electrode layer 196.

This embodiment can be implemented in appropriate combination with thestructures described in the other embodiments.

(Embodiment 5)

In this embodiment, an example of a thin film transistor whosemanufacturing process is partly different from that of Embodiment 1 willbe described with reference to FIG. 10. FIG. 10 is the same as FIG. 1,FIGS. 2A to 2C, FIGS. 3A to 3C, FIGS. 4A and 4B, and FIGS. 5A and 5Bexcept for part of the steps. Thus, the same parts as in FIG. 1, FIGS.2A to 2C, FIGS. 3A to 3C, FIGS. 4A and 4B, and FIGS. 5A and 5B aredenoted by the same reference numerals and detailed description on theparts is omitted.

First, according to Embodiment 1, the gate electrode layer and the gateinsulating layer are formed over a substrate. Then, in the pixelportion, a contact hole which reaches the gate electrode layer is formedin a second photolithography step (not illustrated).

Next, the oxide semiconductor film 130 is formed and then processed intothe island-shaped oxide semiconductor layers 131 and 132 in a thirdphotolithography step.

Next, the oxide semiconductor layers 131 and 132 are dehydrated ordehydrogenated. The temperature of first heat treatment at whichdehydration or dehydrogenation is performed is higher than or equal to400° C. and lower than or equal to 750° C., preferably higher than orequal to 425° C. and lower than or equal to 750° C. Note that in thecase where the temperature of the first heat treatment is 425° C. orhigher, the heat treatment time may be one hour or less, while in thecase where the temperature of the first heat treatment is lower than425° C., the heat treatment time is set to more than one hour. Here, thesubstrate is introduced into an electric furnace which is one example ofheat treatment apparatuses, and the oxide semiconductor layers aresubjected to heat treatment in a nitrogen atmosphere. Then, the oxidesemiconductor layers are not exposed to air and water and hydrogen areprevented from entering the oxide semiconductor layers again. In thismanner, oxide semiconductor layers are formed. Then, a high-purityoxygen gas, a high-purity N₂O gas, or ultra-dry air (having a dew pointof −40° C. or lower, preferably −60° C. or lower) is introduced to thesame furnace and cooling is performed. It is preferable that water,hydrogen, or the like be not contained in the oxygen gas or the N₂O gas.In addition, it is preferable that the oxygen gas or the N₂O gas, whichis introduced into an apparatus for heat treatment, have purity of 6N(99.9999%) or more, preferably 7N (99.99999%) or more; that is, animpurity concentration in the oxygen gas or the N₂O gas is preferably 1ppm or lower, further preferably 0.1 ppm or lower.

The heat treatment apparatus is not limited to the electric furnace,and, for example, may be an RTA (rapid thermal annealing) apparatus suchas a GRTA (gas rapid thermal annealing) apparatus or an LRTA (lamp rapidthermal annealing) apparatus. An LRTA apparatus is an apparatus forheating an object to be processed by radiation of light (anelectromagnetic wave) emitted from a lamp such as a halogen lamp, ametal halide lamp, a xenon arc lamp, a carbon arc lamp, a high-pressuresodium lamp, or a high-pressure mercury lamp. In addition, the LRTAapparatus may be provided with not only a lamp but also a device whichheats an object to be processed by heat conduction or heat radiationfrom a heater such as a resistance heater. GRTA is a method of heattreatment using a high-temperature gas. As the gas, an inert gas whichdoes not react with an object to be processed by heat treatment, forexample, nitrogen or a rare gas such as argon, is used. The heattreatment may be performed by an RTA method at 600° C. to 750° C. forseveral minutes.

In addition, after the first heat treatment for dehydration ordehydrogenation, heat treatment may be performed at higher than or equalto 200° C. and lower than or equal to 400° C., preferably higher than orequal to 200° C. and lower than or equal to 300° C., in an oxygen gasatmosphere or an N₂O gas atmosphere.

The first heat treatment of the oxide semiconductor layers 131 and 132can also be performed on the oxide semiconductor film 130 which has notbeen processed into the island-shaped oxide semiconductor layers. Inthat case, after the first heat treatment, the substrate is taken out ofthe heating device and a photolithography step is performed.

Through the above process, the entire region of the oxide semiconductorfilm is made in an oxygen-excess state, whereby higher resistance(i-type conductivity) is obtained. Accordingly, oxide semiconductorlayers 168 and 198 whose entire region has i-type conductivity areformed.

Next, a fourth photolithography step is performed. Resist masks areformed over the oxide semiconductor layers 168 and 198 and a sourceelectrode layer and a drain electrode layer are formed by a selectiveetching. An oxide insulating film 107 is formed by a sputtering method.

Next, in order to reduce variation in electric characteristics of thethin film transistors, heat treatment (preferably at higher than orequal to 150° C. and lower than 350° C.) may be performed in an inertgas atmosphere or a nitrogen gas atmosphere. For example, heat treatmentmay be performed under a nitrogen atmosphere at 250° C. for an hour.

Next, the protective insulating layer 106 is formed over the oxideinsulating film 107 and the color filter layer 191 is formed over theprotective insulating layer 106 in the pixel portion. The overcoat layer192 is formed so as to cover the color filter layer 191 and theprotective insulating layer 109 is formed so as to cover the protectiveinsulating layer 106 and the overcoat layer 192.

Next, a ninth photolithography step is performed. Resist masks areformed and contact holes which reach the first terminal 121, theconductive layer 162, the drain electrode layer 105 b, and the secondterminal 122 are formed by etching the gate insulating layer 102, theoxide insulating film 107, the protective insulating layer 106, and theprotective insulating layer 109. After a light-transmitting conductivefilm is formed, a tenth photolithography step is performed. Resist masksare formed and selective etching is performed to form the firstelectrode layer 110, the terminal electrode 128, the terminal electrode129, and a wiring layer 145.

This embodiment is an example where the first terminal 121 and theterminal electrode 128 are directly connected to each other without theconnection electrode 120. Further, the drain electrode layer 165 b andthe conductive layer 162 are connected to each other through the wiringlayer 145.

In the capacitor portion, the capacitor 147 is formed from a stack ofthe capacitor wiring layer 108, the gate insulating layer 102, and thecapacitor electrode layer 149 formed in the same step as the sourceelectrode layer and the drain electrode layer.

Through the above steps, a thin film transistor 183 in the drivercircuit portion and a thin film transistor 173 in a pixel portion can beformed over the same substrate.

As in Embodiment 1, the partition 193 is formed and the EL layer 194 andthe second electrode layer 195 are stacked over the first electrodelayer 110, whereby the light-emitting device of this embodiment, whichincludes a light-emitting element, is manufactured (see FIG. 10).

This embodiment can be implemented in appropriate combination with thestructures described in the other embodiments.

(Embodiment 6)

In this embodiment, in the light-emitting device described in any ofEmbodiments 1 to 5, an example of manufacturing an active matrixlight-emitting display device with the use of a thin film transistor anda light-emitting element utilizing electroluminescence will bedescribed.

Light-emitting elements utilizing electroluminescence are classifiedaccording to whether a light-emitting material is an organic compound oran inorganic compound. In general, the former is referred to as anorganic EL element, and the latter is referred to as an inorganic ELelement.

In the organic EL element, by application of voltage to a light-emittingelement, electrons and holes are separately injected from a pair ofelectrodes into a layer containing a light-emitting organic compound,and thus current flows. Then, the carriers (electrons and holes)recombine, so that the light-emitting organic compound is excited. Thelight-emitting organic compound returns to a ground state from theexcited state, thereby emitting light. Owing to such a mechanism, such alight-emitting element is referred to as a current-excitationlight-emitting element.

The inorganic EL elements are classified according to their elementstructures into a dispersion-type inorganic EL element and a thin-filminorganic EL element. The dispersion-type inorganic EL element has alight-emitting layer where particles of a light-emitting material aredispersed in a binder, and its light emission mechanism isdonor-acceptor recombination type light emission which utilizes a donorlevel and an acceptor level. The thin-film inorganic EL element has astructure where a light-emitting layer is sandwiched between dielectriclayers, which are further sandwiched between electrodes, and its lightemission mechanism is localized type light emission that utilizesinner-shell electron transition of metal ions. Note that an example ofan organic EL element as a light-emitting element is described here.

FIG. 19 illustrates an example of a pixel structure to which digitaltime grayscale driving can be applied, as an example of a light-emittingdevice.

The structure and operation of a pixel to which digital time grayscaledriving can be applied are described. Here, one pixel includes twon-channel transistors each of which includes an oxide semiconductorlayer for a channel formation region.

A pixel 6400 includes a switching transistor 6401, a driver transistor6402, a light-emitting element 6404, and a capacitor 6403. A gate of theswitching transistor 6401 is connected to a scan line 6406, a firstelectrode (one of a source electrode and a drain electrode) of theswitching transistor 6401 is connected to a signal line 6405, and asecond electrode (the other of the source electrode and the drainelectrode) of the switching transistor 6401 is connected to a gate ofthe driver transistor 6402. The gate of the driver transistor 6402 isconnected to a power supply line 6407 through the capacitor 6403, afirst electrode of the driver transistor 6402 is connected to the powersupply line 6407, and a second electrode of the driver transistor 6402is connected to a first electrode (pixel electrode) of thelight-emitting element 6404. A second electrode of the light-emittingelement 6404 corresponds to a common electrode 6408. The commonelectrode 6408 is electrically connected to a common potential lineprovided over the same substrate.

The second electrode (common electrode 6408) of the light-emittingelement 6404 is set to a low power supply potential. Note that the lowpower supply potential is a potential in which the low power supplypotential is smaller than a high power supply potential with referenceto the high power supply potential that is set to the power supply line6407. As the low power supply potential, GND, 0 V, or the like may beemployed, for example. A potential difference between the high powersupply potential and the low power supply potential is applied to thelight-emitting element 6404 so that current flows through thelight-emitting element 6404, whereby the light-emitting element 6404emits light. Thus, each potential is set so that the potentialdifference between the high power supply potential and the low powersupply potential is higher than or equal to a forward threshold voltageof the light-emitting element 6404.

When gate capacitance of the driver transistor 6402 is used as asubstitute for the capacitor 6403, the capacitor 6403 can be omitted.The gate capacitance of the driver transistor 6402 may be formed betweena channel region and a gate electrode.

In the case of a voltage-input voltage driving method, a video signal isinput to the gate of the driver transistor 6402 so that the drivertransistor 6402 is completely turned on or off. That is, the drivertransistor 6402 operates in a linear region; thus, voltage higher thanthe voltage of the power supply line 6407 is applied to the gate of thedriver transistor 6402. Note that voltage higher than or equal to“voltage of the power supply line+V_(th) of the driver transistor 6402”is applied to the signal line 6405.

In the case of performing analog grayscale driving instead of digitaltime grayscale driving, the same pixel structure as in FIG. 19 can beused by changing signal input.

In the case of performing the analog grayscale driving, a voltage higherthan or equal to voltage which is the sum of the forward voltage of thelight-emitting element 6404 and V_(th) of the driver transistor 6402 isapplied to the gate of the driver transistor 6402. The forward voltageof the light-emitting element 6404 refers to a voltage at which adesired luminance is obtained, and includes at least forward thresholdvoltage. By inputting a video signal to enable the driver transistor6402 to operate in a saturation region, current can flow through thelight-emitting element 6404. In order that the driver transistor 6402can operate in the saturation region, the potential of the power supplyline 6407 is set higher than the gate potential of the driver transistor6402. With an analog video signal, current in accordance with the videosignal flows through the light-emitting element 6404, and the analoggrayscale driving can be performed.

The pixel structure illustrated in FIG. 19 is not limited thereto. Forexample, a switch, a resistor, a capacitor, a transistor, a logiccircuit, or the like may be added to the pixel illustrated in FIG. 19.

Next, structures of the light-emitting element are described withreference to FIGS. 20A to 20C. Here, a cross-sectional structure of apixel is described by taking an n-channel driving TFT as an example.Driving TFTs 7001, 7011, and 7021 used in light-emitting devicesillustrated in FIGS. 20A, 20B, and 20C, respectively, can be formed in amanner similar to that of the thin film transistor described in any ofEmbodiments 1 to 5, and are highly reliable thin film transistors eachincluding an oxide semiconductor layer.

In order to extract light emitted from the light-emitting element, atleast one of an anode and a cathode is required to transmit light. Athin film transistor and a light-emitting element are formed over asubstrate. A light-emitting element can have a top emission structure inwhich light is extracted through the surface opposite to the substrate;a bottom emission structure in which light is extracted through thesurface on the substrate side; or a dual emission structure in whichlight is extracted through the surface opposite to the substrate and thesurface on the substrate side. The pixel structure can be applied to alight-emitting element having any of these emission structures.

A light-emitting element having the bottom emission structure will bedescribed with reference to FIG. 20A.

FIG. 20A is a cross-sectional view of a pixel in the case where thedriver TFT 7011 is an n-channel transistor and light is emitted from alight-emitting element 7012 to a first electrode layer 7013 side. InFIG. 20A, the first electrode layer 7013 of the light-emitting element7012 is formed over a light-transmitting conductive film 7017 which iselectrically connected to the driver TFT 7011, and an EL layer 7014 anda second electrode layer 7015 are stacked in this order over the firstelectrode layer 7013. Note that the conductive film 7017 is electricallyconnected to a drain electrode layer of the driver TFT 7011 through acontact hole formed in a protective insulating layer 7035, a protectiveinsulating layer 7032, and an oxide insulating layer 7031.

As the light-emitting conductive film 7017, a light-transmittingconductive film such as a film of indium oxide including tungsten oxide,indium zinc oxide including tungsten oxide, indium oxide includingtitanium oxide, indium tin oxide including titanium oxide, indium tinoxide, indium zinc oxide, or indium tin oxide to which silicon oxide isadded can be used.

Further, a variety of materials can be used for the first electrodelayer 7013 of the light-emitting element. For example, in the case wherethe first electrode layer 7013 is used as a cathode, a material having alow work function such as an alkali metal such as Li or Cs, an alkalineearth metal such as Mg, Ca, or Sr, an alloy containing any of them(e.g., Mg:Ag, Al:Li), or a rare earth metal such as Yb or Er ispreferable. In FIG. 20A, the first electrode layer 7013 is formed tohave a thickness through which light can be transmitted (preferably,approximately 5 nm to 30 nm). For example, an aluminum film with athickness of 20 nm is used as the first electrode layer 7013.

Alternatively, a light-transmitting conductive film and an aluminum filmmay be stacked and then selectively etched so as to form thelight-transmitting conductive film 7017 and the first electrode layer7013. In this case, the etching can be performed using the same mask,which is preferable.

Further, the periphery of the first electrode layer 7013 is covered witha partition 7019. The partition 7019 is formed using a film of anorganic resin such as polyimide, acrylic, polyamide, or epoxy, aninorganic insulating film, or organic polysiloxane. It is particularlypreferable that the partition 7019 be formed using a photosensitiveresin material to have an opening portion over the first electrode layer7013 so that a sidewall of the opening portion is formed as a tiltedsurface with continuous curvature. When a photosensitive resin materialis used for the partition 7019, a step of forming a resist mask can beomitted.

Further, the EL layer 7014 formed over the first electrode layer 7013and the partition 7019 may include at least a light-emitting layer andbe formed using a single layer or a plurality of layers stacked. Whenthe EL layer 7014 is formed using a plurality of layers, anelectron-injection layer, an electron-transport layer, a light-emittinglayer, a hole-transport layer, and a hole-injection layer are stacked inthis order over the first electrode layer 7013 functioning as a cathode.Note that it is not necessary to form all of these layers.

The stacking order is not limited to the above order. The firstelectrode layer 7013 may function as an anode and a hole-injectionlayer, hole-transport layer, a light-emitting layer, anelectron-transport layer, and an electron-injection layer may be stackedin this order over the first electrode layer 7013. Note that from apower consumption standpoint, it is preferable to make the firstelectrode layer 7013 function as a cathode and to stack anelectron-injection layer, an electron-transport layer, a light-emittinglayer, a hole-transport layer, and a hole-injection layer in this orderover the first electrode layer 7013 because increase in driving voltageof the driver circuit portion can be suppressed and thus powerconsumption can be reduced.

Further, a variety of materials can be used for the second electrodelayer 7015 formed over the EL layer 7014. For example, in the case wherethe second electrode layer 7015 is used as an anode, a material having ahigh work function, such as ZrN, Ti, W, Ni, Pt, or Cr, or a transparentconductive material such as ITO, IZO, or ZnO is preferable. Further,over the second electrode layer 7015, a light-blocking film 7016 isformed using a metal blocking light, a metal reflecting light, or thelike. In this embodiment, an ITO film is used as the second electrodelayer 7015 and a Ti film is used as the light-blocking film 7016.

The light-emitting element 7012 corresponds to a region where the ELlayer 7014 including a light-emitting layer is sandwiched with the firstelectrode layer 7013 and the second electrode layer 7015. In the case ofthe element structure illustrated in FIG. 20A, light is emitted from thelight-emitting element 7012 to the first electrode layer 7013 side topass through a color filter layer 7033 to the outside as indicated by anarrow.

The color filter layer 7033 is formed by a droplet discharge method suchas an ink-jet method, a printing method, an etching method with the useof a photolithography technique, or the like.

The color filter layer 7033 is covered with an overcoat layer 7034 andthe protective insulating layer 7035 is further formed thereover. Notethat although the overcoat layer 7034 is illustrated to have a smallthickness in FIG. 20A, the overcoat layer 7034 has a function ofreducing roughness caused by the color filter layer 7033.

Next, a light-emitting element having the dual emission structure willbe described with reference to FIG. 20B.

In FIG. 20B, a first electrode layer 7023 of a light-emitting element7022 is formed over a light-transmitting conductive film 7027 which iselectrically connected to the driver TFT 7021, and an EL layer 7024 anda second electrode layer 7025 are stacked in this order over the firstelectrode layer 7023. Note that the conductive film 7027 is electricallyconnected to a drain electrode layer of the driver TFT 7021 through acontact hole formed in a protective insulating layer 7045, a protectiveinsulating layer 7042, and an oxide insulating layer 7041.

As the light-transmitting conductive film 7027, a light-transmittingconductive film such as a film of indium oxide including tungsten oxide,indium zinc oxide including tungsten oxide, indium oxide includingtitanium oxide, indium tin oxide including titanium oxide, indium tinoxide, indium zinc oxide, or indium tin oxide to which silicon oxide isadded can be used.

A variety of materials can be used for the first electrode layer 7023.For example, in the case where the first electrode layer 7023 is used asa cathode, a material having a low work function such as an alkali metalsuch as Li or Cs, an alkaline earth metal such as Mg, Ca, or Sr, analloy containing any of them (e.g., Mg:Ag, Al:Li), or a rare earth metalsuch as Yb or Er is preferable. In this embodiment, the first electrodelayer 7023 functions as a cathode and is formed to have a thicknessthrough which light can be transmitted (preferably, approximately 5 nmto 30 nm). For example, an aluminum film with a thickness of 20 nm isused as the cathode.

Alternatively, a light-transmitting conductive film and an aluminum filmmay be stacked and then selectively etched so as to form thelight-transmitting conductive film 7027 and the first electrode layer7023. In this case, the etching can be performed using the same mask,which is preferable.

Further, the periphery of the first electrode layer 7023 is covered witha partition 7029. The partition 7029 is formed using a film of anorganic resin such as polyimide, acrylic, polyamide, or epoxy, aninorganic insulating film, or organic polysiloxane. It is particularlypreferable that the partition 7029 be formed using a photosensitiveresin material to have an opening portion over the first electrode layer7023 so that a sidewall of the opening portion is formed as a tiltedsurface with continuous curvature. When a photosensitive resin materialis used for the partition 7029, a step of forming a resist mask can beomitted.

Further, the EL layer 7024 formed over the first electrode layer 7023and the partition 7029 may include at least a light-emitting layer andbe formed using a single layer or a plurality of layers stacked. Whenthe EL layer 7024 is formed using a plurality of layers, anelectron-injection layer, an electron-transport layer, a light-emittinglayer, a hole-transport layer, and a hole-injection layer are stacked inthis order over the first electrode layer 7023 functioning as a cathode.Note that it is not necessary to form all of these layers.

The stacking order is not limited to the above order. The firstelectrode layer 7023 may function as an anode and a hole-injectionlayer, hole-transport layer, a light-emitting layer, anelectron-transport layer, and an electron-injection layer may be stackedin this order over the anode. Note that from a power consumptionstandpoint, it is preferable to make the first electrode layer 7023function as a cathode and to stack an electron-injection layer, anelectron-transport layer, a light-emitting layer, a hole-transportlayer, and a hole-injection layer in this order over the cathode becausepower consumption can be reduced.

Further, a variety of materials can be used for the second electrodelayer 7025 formed over the EL layer 7024. For example, in the case wherethe second electrode layer 7025 is used as an anode, a material having ahigh work function, for example, a transparent conductive material suchas ITO, IZO, or ZnO, is preferably used. In this embodiment, the secondelectrode layer 7025 is used as an anode and an ITO film includingsilicon oxide is formed.

The light-emitting element 7022 corresponds to a region where the ELlayer 7024 including a light-emitting layer is sandwiched with the firstelectrode layer 7023 and the second electrode layer 7025. In the case ofthe element structure illustrated in FIG. 20B, light is emitted from thelight-emitting element 7022 to both the second electrode layer 7025 sideand the first electrode layer 7023 side as indicated by arrows.

A color filter layer 7043 is formed by a droplet discharge method suchas an ink-jet method, a printing method, an etching method with the useof a photolithography technique, or the like.

The color filter layer 7043 is covered with an overcoat layer 7044 andthe protective insulating layer 7045 is further formed thereover.

Note that when a light-emitting element having a dual emission structureis used and full color display is performed on both display surfaces,light from the second electrode layer 7025 side does not pass throughthe color filter layer 7043; therefore, a sealing substrate providedwith another color filter layer is preferably provided on the secondelectrode layer 7025.

Next, a light-emitting element having a top emission structure will bedescribed with reference to FIG. 20C.

FIG. 20C is a cross-sectional view of a pixel in the case where thedriver TFT 7001 is an n-channel transistor and light is emitted from alight-emitting element 7002 to a second electrode layer 7005 side. InFIG. 20C, a first electrode layer 7003 of the light-emitting element7002, which is electrically connected to the TFT 7001, is formed, and anEL layer 7004 and the second electrode layer 7005 are stacked in thisorder over the first electrode layer 7003.

Further, a variety of materials can be used for the first electrodelayer 7003. For example, in the case where the first electrode layer7003 is used as a cathode, a material having a low work function such asan alkali metal such as Li or Cs, an alkaline earth metal such as Mg,Ca, or Sr, an alloy containing any of them (e.g., Mg:Ag, Al:Li), or arare earth metal such as Yb or Er is preferable.

Further, the periphery of the first electrode layer 7003 is covered witha partition 7009. The partition 7009 is formed using a film of anorganic resin such as polyimide, acrylic, polyamide, or epoxy, aninorganic insulating film, or organic polysiloxane. It is particularlypreferable that the partition 7009 be formed using a photosensitiveresin material to have an opening portion over the first electrode layer7003 so that a sidewall of the opening portion is formed as a tiltedsurface with continuous curvature. When a photosensitive resin materialis used for the partition 7009, a step of forming a resist mask can beomitted.

Further, the EL layer 7004 formed over the first electrode layer 7003and the partition 7009 may include at least a light-emitting layer andbe formed using a single layer or a plurality of layers stacked. Whenthe EL layer 7004 is formed using a plurality of layers, anelectron-injection layer, an electron-transport layer, a light-emittinglayer, a hole-transport layer, and a hole-injection layer are stacked inthis order over the first electrode layer 7003 used as a cathode. Notethat it is not necessary to form all of these layers.

The stacking order is not limited to the above order. A hole-injectionlayer, hole-transport layer, a light-emitting layer, anelectron-transport layer, and an electron-injection layer may be stackedin this order over the first electrode layer 7003 used as an anode.

In FIG. 20C, a hole-injection layer, a hole-transport layer, alight-emitting layer, an electron-transport layer, and anelectron-injection layer are stacked in this order over a stacked filmin which a Ti film, an aluminum film, and a Ti film are formed in thisorder, and thereover, a stacked layer of a Mg:Ag alloy thin film and anITO film is formed.

Note that when the TFT 7001 is an n-type transistor, it is preferable tostack an electron-injection layer, an electron-transport layer, alight-emitting layer, a hole-transport layer, and a hole-injection layerin this order over the first electrode layer 7003 because increase involtage of the driver circuit can be suppressed and thus powerconsumption can be reduced.

The second electrode layer 7005 is formed using a light-transmittingconductive film. For example, a light-transmitting conductive film suchas a film of indium oxide including tungsten oxide, indium zinc oxideincluding tungsten oxide, indium oxide including titanium oxide, indiumtin oxide including titanium oxide, indium tin oxide, indium zinc oxide,or indium tin oxide to which silicon oxide is added can be used.

The light-emitting element 7002 corresponds to a region where the ELlayer 7004 including a light-emitting layer is sandwiched with the firstelectrode layer 7003 and the second electrode layer 7005. In the case ofthe pixel illustrated in FIG. 20C, light is emitted from thelight-emitting element 7002 to the second electrode layer 7005 side asindicated by an arrow.

Further, in FIG. 20C, a drain electrode layer of the TFT 7001 iselectrically connected to the first electrode layer 7003 through acontact hole formed in an oxide insulating layer 7051, a protectiveinsulating layer 7052, and a protective insulating layer 7055. Aplanarizing insulating layer 7053 can be formed using a resin materialsuch as polyimide, acrylic, benzocyclobutene, polyamide, or epoxy. Inaddition to such resin materials, it is also possible to use a lowdielectric constant material (a low-k material), a siloxane-based resin,PSG (phosphosilicate glass), BPSG (borophosphosilicate glass), or thelike. Note that the planarizing insulating layer 7053 may be formed bystacking a plurality of insulating films formed using these materials.There is no particular limitation on a method for forming theplanarizing insulating layer 7053. The planarizing insulating layer 7053can be formed, depending on the material, with a method such as asputtering method, an SOG method, a spin coating method, a dippingmethod, a spray coating method, or a droplet discharge method (e.g., anink-jet method, screen printing, or offset printing), or with a meanssuch as a doctor knife, a roll coater, a curtain coater, or a knifecoater.

Further, the partition 7009 is formed to insulate the first electrodelayer 7003 from a first electrode layer of an adjacent pixel. Thepartition 7009 is formed using a film of an organic resin such aspolyimide, acrylic, polyamide, or epoxy, an inorganic insulating film,or organic polysiloxane. It is particularly preferable that thepartition 7009 be formed using a photosensitive resin material to havean opening portion over the first electrode layer 7003 so that asidewall of the opening portion is formed as a tilted surface withcontinuous curvature. When a photosensitive resin material is used forthe partition 7009, a step of forming a resist mask can be omitted.

In the structure in FIG. 20C, when full color display is performed, forexample, the light-emitting element 7002 is used as a greenlight-emitting element, one of the adjacent light-emitting elements isused as a red light-emitting element, and the other is used as a bluelight-emitting element. Alternatively, a light-emitting display devicecapable of full color display may be manufactured using four kinds oflight-emitting elements, which include a white light emitting-element aswell as the three kinds of the light-emitting elements.

Alternatively, in the structure in FIG. 20C, a light-emitting displaydevice capable of full color display may be manufactured in such a waythat all of the plurality of light-emitting elements which are arrangedare white light-emitting elements and a sealing substrate having a colorfilter or the like is arranged over the light-emitting element 7002.When a material which exhibits a single color such as white is formedand then combined with a color filter or a color conversion layer, fullcolor display can be performed.

The examples in which the first electrode layer is in direct contactwith the thin film transistor are illustrated in FIGS. 20A to 20C;however, as described in Embodiment 4, the drain electrode layer of thethin film transistor may be electrically connected to the firstelectrode layer through the connection electrode layer. The thin filmtransistors described in any of Embodiments 2, 3, and 5 may be used asthe TFTs 7001, 7011, and 7021.

Needless to say, display of monochromatic light emission can also beperformed. For example, a lighting device may be formed with the use ofwhite light emission; alternatively, an area-color light-emitting devicemay be formed with the use of monochromatic light emission.

If necessary, an optical film such as a polarizing film including acircularly polarizing plate may be provided.

Note that, although the organic EL element is described here as thelight-emitting element, an inorganic EL element can also be provided asa light-emitting element.

Note that the example is described in which the thin film transistor(the driver TFT) which controls the driving of a light-emitting elementis electrically connected to the light-emitting element; however, astructure may be employed in which a TFT for current control isconnected between a driver TFT and a light-emitting element.

This embodiment can be combined with any of the other embodiments asappropriate.

(Embodiment 7)

In this embodiment, an example of an element structure of thelight-emitting element described in any of Embodiments 1 to 6 will bedescribed.

In the element structure illustrated in FIG. 21A, an EL layer 1003including a light-emitting region is sandwiched between a pair ofelectrodes (a first electrode 1001 and a second electrode 1002). Notethat the first electrode 1001 is used as an anode and the secondelectrode 1002 is used as a cathode as an example in the followingdescription of this embodiment.

The EL layer 1003 includes at least a light-emitting layer and may havea stacked structure including a functional layer in addition to thelight-emitting layer. As the functional layer other than thelight-emitting layer, a layer containing a substance having a highhole-injection property, a substance having a high hole-transportproperty, a substance having a high electron-transport property, asubstance having a high electron-injection property, a bipolar substance(a substance having high electron-transport and hole-transportproperties), or the like can be used. Specifically, functional layerssuch as a hole-injection layer, a hole-transport layer, anelectron-transport layer, and an electron-injection layer can be used incombination as appropriate.

The light-emitting element illustrated in FIG. 21A emits light whencurrent flows because of the potential difference generated between thefirst electrode 1001 and the second electrode 1002, and holes andelectrons are recombined in the EL layer 1003. That is, a light-emittingregion is formed in the EL layer 1003.

Light emission is extracted outside through one of or both the firstelectrode 1001 and the second electrode 1002. Therefore, either or bothof the first electrode 1001 and the second electrode 1002 is formedusing a light-transmitting substance.

Note that a plurality of EL layers may be stacked between the firstelectrode 1001 and the second electrode 1002 as illustrated in FIG. 21B.In the case where n (n is a natural number of 2 or more) layers arestacked, a charge generation layer 1004 is preferably provided betweeneach m-th (m is a natural number of 1 and more and n−1 or less) EL layerand each (m+1)-th EL layer.

The charge generation layer 1004 can be formed using a compositematerial of an organic compound and a metal oxide, a metal oxide, or acomposite material of an organic compound and an alkali metal, analkaline earth metal, or a compound thereof. Alternatively, thesematerials can be combined as appropriate. The composite material of anorganic compound and a metal oxide includes, for example, an organiccompound and a metal oxide such as V₂O₅, MoO₃, or WO₃. As the organiccompound, various compounds such as an aromatic amine compound, acarbazole derivative, aromatic hydrocarbon, and a high molecularcompound (oligomer, dendrimer, polymer, or the like) can be used. As theorganic compound, it is preferable to use the organic compound which hasa hole-transport property and has a hole mobility of 10⁻⁶ cm²/Vs orhigher. However, substances other than the above-described materials mayalso be used as long as the substances have higher hole-transportproperties than electron-transport properties. These materials used forthe charge generation layer 1004 are excellent in carrier-injectionproperty and carrier-transport property, and thus, a light-emittingelement can be driven with low current and with low voltage.

Note that the charge generation layer 1004 may be formed in acombination of a composite material of an organic compound and a metaloxide with another material. For example, a layer containing a compositematerial of the organic compound and the metal oxide may be combinedwith a layer containing a compound of a substance selected fromsubstances having an electron-donation property and a compound having ahigh electron-transport property. Moreover, a layer containing acomposite material of the organic compound and the metal oxide may becombined with a transparent conductive film.

As for a light-emitting element having such a structure, problems suchas energy transfer and quenching are unlikely to occur, and alight-emitting element which has both high light emission efficiency andlong lifetime can be easily obtained due to expansion in the choice ofmaterials. Moreover, a light-emitting element which providesphosphorescence from one of the EL layers and fluorescence from theother of the EL layers can be readily obtained.

Note that the charge generation layer 1004 has a function of injectingholes to one EL layer 1003 which is formed in contact with the chargegeneration layer 1004 and a function of injecting electrons to the otherEL layer 1003 which is formed in contact with the charge generationlayer 1004, when voltage is applied to the first electrode 1001 and thesecond electrode 1002.

The light-emitting element shown in FIG. 21B can provide a variety ofemission colors by changing the type of the light-emitting substancethat is used for the light-emitting layer. In addition, a plurality oflight-emitting substances of different colors is used as thelight-emitting substance, whereby light emission having a broad spectrumor white light emission can also be obtained.

In the case of obtaining white color light using the light-emittingelement shown in FIG. 21B, as for the combination of a plurality oflight-emitting layers, a structure for emitting white light includingred light, blue light, and green light may be used. For example, thestructure may include a first EL layer containing a blue fluorescentsubstance as a light-emitting substance and a second EL layer containinggreen and red phosphorescent substances as light-emitting substances.Alternatively, the structure may include a first EL layer exhibiting redlight emission, a second EL layer exhibiting green light emission, and athird EL layer exhibiting blue light emission. Also with a structureincluding light-emitting layers emitting light of complementary colors,white light emission can be obtained. When light emission from the firstEL layer and light emission from the second EL layer have complementarycolors to each other in an element including two EL layers stacked, thecombination of colors are as follows: blue and yellow, blue-green andred, and the like.

Note that in the structure of the above-mentioned stacked element, byproviding the charge generation layer between the stacked EL layers, theelement can have long lifetime in a high luminance region while keepingthe current density low. In addition, the voltage drop due to resistanceof the electrode material can be reduced, whereby uniform light emissionin a large area is possible.

This embodiment can be combined with the structures disclosed in theother embodiments as appropriate.

(Embodiment 8)

In this embodiment, the appearance and a cross section of alight-emitting display panel (also referred to as a light-emittingpanel) will be described with reference to FIGS. 22A and 22B. FIG. 22Ais a plan view of a panel in which a thin film transistor and alight-emitting element which are formed over a first substrate aresealed between the first substrate and a second substrate with asealant. FIG. 22B is a cross-sectional view taken along line H-I in FIG.22A.

A sealant 4505 is provided so as to surround a pixel portion 4502,signal line driver circuits 4503 a and 4503 b, and scan line drivercircuits 4504 a and 4504 b which are provided over a first substrate4501. In addition, a second substrate 4506 is provided over the pixelportion 4502, the signal line driver circuits 4503 a and 4503 b, and thescan line driver circuits 4504 a and 4504 b. Accordingly, the pixelportion 4502, the signal line driver circuits 4503 a and 4503 b, and thescan line driver circuits 4504 a and 4504 b are sealed together with afiller 4507, by the first substrate 4501, the sealant 4505, and thesecond substrate 4506. It is preferable that a panel be packaged(sealed) with a protective film (such as a bonding film or anultraviolet curable resin film) or a cover material with highair-tightness and little degasification so that the panel is not exposedto the outside air.

The pixel portion 4502, the signal line driver circuits 4503 a and 4503b, and the scan line driver circuits 4504 a and 4504 b formed over thefirst substrate 4501 each include a plurality of thin film transistors,and a thin film transistor 4510 included in the pixel portion 4502 and athin film transistor 4509 included in the signal line driver circuit4503 a are illustrated as an example in FIG. 22B.

Any of the highly reliable thin film transistors including the oxidesemiconductor layers, which are described in Embodiments 1 to 5, can beused as the thin film transistors 4509 and 4510. As the thin filmtransistor 4509 for the driver circuit, any of the thin film transistors180, 181, and 182 which are described in Embodiments 1 to 5 can be used.As the thin film transistor 4510 for the pixel, any of the thin filmtransistors 170, 171, and 172 which are described in Embodiments 1 to 5can be used. In this embodiment, the thin film transistors 4509 and 4510are n-channel thin film transistors.

A conductive layer 4540 is provided over an insulating layer 4544 so asto overlap with a channel formation region in an oxide semiconductorlayer of the thin film transistor 4509 for the driver circuit. Theconductive layer 4540 is provided so as to overlap with the channelformation region of the oxide semiconductor layer, whereby the amount ofchange in the threshold voltage of the thin film transistor 4509 beforeand after BT test can be reduced. Further, a potential of the conductivelayer 4540 may be the same as or different from that of the gateelectrode layer of the thin film transistor 4509. The conductive layer4540 can function also as a second gate electrode layer. Alternatively,the potential of the conductive layer 4540 may be GND or 0 V, or theconductive layer 4540 may be in a floating state.

Although not illustrated, a protective insulating layer such as theprotective insulating layer 106 in Embodiment 1 may be provided betweenan oxide insulating layer 4542 and the insulating layer 4544.

The thin film transistor 4510 is electrically connected to a firstelectrode layer 4517.

The oxide insulating layer 4542 may be formed using a material andmethod which are similar to those of the oxide insulating film 107described in Embodiment 1.

A color filter layer 4545 is formed over the oxide insulating layer 4542so as to overlap with a light-emitting region of a light-emittingelement 4511.

Further, in order to reduce the surface roughness of the color filterlayer 4545, the color filter layer 4545 is covered with an overcoatlayer 4543 functioning as a planarizing insulating film.

Further, an insulating layer 4544 is formed over the overcoat layer4543. The insulating layer 4544 may be formed using a material and amethod which are similar to those of the protective insulating layer 109described in Embodiment 1.

Moreover, reference numeral 4511 denotes a light-emitting element. Thefirst electrode layer 4517 which is a pixel electrode included in thelight-emitting element 4511 is electrically connected to a source ordrain electrode layer of the thin film transistor 4510. Note thatalthough the light-emitting element 4511 has a stacked structure of thefirst electrode layer 4517, an electroluminescent layer 4512, and asecond electrode layer 4513, the structure of the light-emitting element4511 is not limited to the structure described in this embodiment. Thestructure of the light-emitting element 4511 can be changed asappropriate depending on the direction in which light is extracted fromthe light-emitting element 4511, or the like.

A partition 4520 is formed using an organic resin film, an inorganicinsulating film, or organic polysiloxane. It is particularly preferablethat the partition 4520 be formed using a photosensitive material and anopening be formed over the first electrode layer 4517 so that a sidewallof the opening is formed as an inclined surface with continuouscurvature.

The electroluminescent layer 4512 may be formed with a single layer or aplurality of layers stacked.

A protective film may be formed over the second electrode layer 4513 andthe partition 4520 in order to prevent entry of oxygen, hydrogen,moisture, carbon dioxide, or the like into the light-emitting element4511. As the protective film, a silicon nitride film, a silicon nitrideoxide film, a DLC film, or the like can be formed.

In addition, a variety of signals and potentials are supplied to thesignal line driver circuits 4503 a and 4503 b, the scan line drivercircuits 4504 a and 4504 b, or the pixel portion 4502 from FPCs 4518 aand 4518 b.

A connection terminal electrode 4515 is formed from the same conductivefilm as the first electrode layer 4517 included in the light-emittingelement 4511, and a terminal electrode 4516 is formed from the sameconductive film as the source and drain electrode layers included in thethin film transistor 4509.

The connection terminal electrode 4515 is electrically connected to aterminal included in the FPC 4518 a via an anisotropic conductive film4519.

The second substrate located in the direction in which light isextracted from the light-emitting element 4511 needs to have alight-transmitting property. In that case, a light-transmitting materialsuch as a glass plate, a plastic plate, a polyester film, or an acrylicfilm is used for the second substrate 4506.

As the filler 4507, an ultraviolet curable resin or a thermosettingresin can be used, in addition to an inert gas such as nitrogen orargon. For example, PVC (polyvinyl chloride), acrylic, polyimide, anepoxy resin, a silicone resin, PVB (polyvinyl butyral), or EVA (ethylenevinyl acetate) can be used. For example, nitrogen is used for thefiller.

In addition, if needed, an optical film such as a polarizing plate, acircularly polarizing plate (including an elliptically polarizingplate), a retardation plate (a quarter-wave plate or a half-wave plate),or a color filter may be provided as appropriate on a light-emittingsurface of the light-emitting element. Further, the polarizing plate orthe circularly polarizing plate may be provided with an anti-reflectionfilm. For example, anti-glare treatment may be performed by whichreflected light can be diffused by projections and depressions on thesurface so that the glare can be reduce.

The signal line driver circuits 4503 a and 4503 b and the scan linedriver circuits 4504 a and 4504 b may be mounted as driver circuitsformed using a single crystal semiconductor film or a polycrystallinesemiconductor film over a substrate separately prepared. Alternatively,only the signal line driver circuits or part thereof, or the scan linedriver circuits or part thereof may be separately formed and mounted.This embodiment is not limited to the structure illustrated in FIGS. 22Aand 22B.

Through the above steps, a highly reliable light-emitting device(display panel) as a semiconductor device can be manufactured.

This embodiment can be implemented in appropriate combination with thestructures described in the other embodiments.

(Embodiment 9)

In this embodiment, an example is described below in which at least someof driver circuits and a thin film transistor provided in a pixelportion are formed over the same substrate.

The thin film transistor provided in the pixel portion is formed inaccordance with Embodiments 1 to 5. The thin film transistors describedin Embodiments 1 to 5 are n-channel TFTs; therefore, some of drivercircuits which can be formed using n-channel TFTs are formed over thesame substrate as the thin film transistor of the pixel portion.

FIG. 12A illustrates an example of a block diagram of an active matrixdisplay device. The display device includes a pixel portion 5301, afirst scan line driver circuit 5302, a second scan line driver circuit5303, and a signal line driver circuit 5304 over a substrate 5300. Inthe pixel portion 5301, a plurality of signal lines which are extendedfrom the signal line driver circuit 5304 and a plurality of scan lineswhich are extended from the first scan line driver circuit 5302 and thesecond scan line driver circuit 5303 are provided. Note that pixelswhich include display elements are arranged in matrix in regions wherethe scan lines and the signal lines are crossed. In addition, thesubstrate 5300 of the display device is connected to a timing controlcircuit 5305 (also referred to as a controller or a control IC) througha connection portion such as a flexible printed circuit (FPC).

In FIG. 12A, the first scan line driver circuit 5302, the second scanline driver circuit 5303, and the signal line driver circuit 5304 areformed over the same substrate 5300 as the pixel portion 5301.Therefore, the number of components of a driver circuit which isprovided outside and the like is reduced, which leads to cost reduction.Further, the number of connections in the connection portion can bereduced by extending wirings in the case where a driver circuit isprovided outside the substrate 5300, which leads to improvement inreliability or improvement in a yield.

The timing control circuit 5305 supplies, for example, a first scan linedriver circuit start signal (GSP1) and a scan line driver circuit clocksignal (GCLK1) to the first scan line driver circuit 5302. The timingcontrol circuit 5305 supplies, for example, a second scan line drivercircuit start signal (GSP2, also referred to as a start pulse) and ascan line driver circuit clock signal (GCLK2) to the second scan linedriver circuit 5303. The timing control circuit 5305 supplies a signalline driver circuit start signal (SSP), a signal line driver circuitclock signal (SCLK), video signal data (DATA, also simply referred to asa video signal), and a latch signal (LAT) to the signal line drivercircuit 5304. Note that each clock signal may be a plurality of clocksignals whose phases are shifted or may be supplied together with aninverted clock signal (CKB) which is obtained by inverting the clocksignal. Note that one of the first scan line driver circuit 5302 and thesecond scan line driver circuit 5303 can be eliminated.

FIG. 12B illustrates a structure in which circuits with low drivingfrequency (e.g., the first scan line driver circuit 5302 and the secondscan line driver circuit 5303) are formed over the same substrate 5300as the pixel portion 5301 and the signal line driver circuit 5304 isformed over a substrate which is different from the pixel portion 5301.With this structure, a driver circuit formed over the substrate 5300 canbe formed using a thin film transistor with lower field effect mobilityas compared to that of a transistor formed using a single crystalsemiconductor. Thus, increase in size of the display device, reductionin cost, improvement in yield, or the like can be achieved.

The thin film transistors described in Embodiments 1 to 5 are n-channelTFTs. FIGS. 13A and 13B illustrate an example of a structure andoperation of a signal line driver circuit which is formed usingn-channel TFTs.

The signal line driver circuit includes a shift register 5601 and aswitching circuit 5602. The switching circuit 5602 includes a pluralityof switching circuits 5602_1 to 5602_N (N is a natural number). Theswitching circuits 5602_1 to 5602_N each include a plurality of thinfilm transistors 5603_to 5603_k (k is a natural number). An examplewhere the thin film transistors 5603_1 to 5603_k are n-channel TFTs isdescribed.

A connection relation in the signal line driver circuit is describedtaking the switching circuit 5602_1 as an example. First terminals ofthe thin film transistors 5603_1 to 5603_k are connected to wirings5604_1 to 5604_k, respectively. Second terminals of the thin filmtransistors 5603_1 to 5603_k are connected to signal lines S1 to Sk,respectively. Gates of the thin film transistors 5603_1 to 5603_k areconnected to a wiring 5605_1.

The shift register 5601 has a function of sequentially outputtingH-level signals (also referred to as H signals or signals at high powersupply potential level) to the wirings 5605_1 to 5605_N and sequentiallyselecting the switching circuits 5602_1 to 5602_N.

The switching circuit 5602_1 has a function of controlling a conductionstate between the wirings 5604_1 to 5604_k and the signal lines S1 to Sk(electrical continuity between the first terminals and the secondterminals), that is, a function of controlling whether potentials of thewirings 5604_1 to 5604_k are supplied to the signal lines S1 to Sk. Inthis manner, the switching circuit 5602_1 functions as a selector.Further, the thin film transistors 5603_1 to 5603_k each have functionsof controlling conduction states between the wirings 5604-1 to 5604_kand the signal lines S1 to Sk, that is, functions of supplying thepotentials of the wirings 5604_1 to 5604_k to the signal lines S1 to Sk.In this manner, each of the thin film transistors 5603_1 to 5603_kfunctions as a switch.

Note that video signal data (DATA) is input to each of the wirings5604_1 to 5604_k. The video signal data (DATA) is an analog signalcorresponding to an image signal or image data in many cases.

Next, operation of the signal line driver circuit in FIG. 13A isdescribed with reference to a timing chart in FIG. 13B. FIG. 13Billustrates examples of signals Sout_1 to Sout_N and signals Vdata_1 toVdata_k. The signals Sout_1 to Sout_N are examples of output signalsfrom the shift register 5601, and the signals Vdata_1 to Vdata_k areexamples of signals input to the wirings 5604_1 to 5604_k. Note that oneoperation period of the signal line driver circuit corresponds to onegate selection period in a display device. For example, one gateselection period is divided into periods T1 to TN. Each of the periodsT1 to TN is a period during which the video signal data (DATA) iswritten to pixels in a selected row.

Note that as for structures shown in drawings and the like of thisembodiment, distortion in signal waveforms and the like are exaggeratedfor simplicity in some cases. Thus, the scale is not necessarily limitedto that illustrated.

In the periods T1 to TN, the shift register 5601 sequentially outputsH-level signals to the wirings 5605_1 to 5605_N. For example, in theperiod T1, the shift register 5601 outputs the H-level signal to thewiring 5605_1. Then, the thin film transistors 5603_1 to 5603_k areturned on, so that the wirings 5604_1 to 5604_k and the signal lines S1to Sk are brought into conduction. In this case, Data (S1) to Data (Sk)are input to the wirings 5604_1 to 5604_k, respectively. The Data (S1)to Data (Sk) are input to pixels in a selected row in first to k-thcolumns through the thin film transistors 5603_1 to 5603_k,respectively. Thus, in the periods T1 to TN, video signal data (DATA) issequentially written to the pixels in the selected row by k columns.

By writing video signal data (DATA) to pixels by a plurality of columnsas described above, the number of video signal data (DATA) or the numberof wirings can be reduced. Accordingly, the number of connections to anexternal circuit can be reduced. By writing video signals to pixels by aplurality of columns, writing time can be extended and insufficientwriting of video signals can be prevented.

Note that as the shift register 5601 and the switching circuit 5602, acircuit including the thin film transistor described in any ofEmbodiments 1 to 5 can be used.

One mode of a shift register which is used for part of a scan linedriver circuit and/or a signal line driver circuit is described withreference to FIGS. 14A to 14C and FIGS. 15A and 15B.

The scan line driver circuit includes a shift register. The scan linedriver circuit may also include a level shifter, a buffer, or the likein some cases. In the scan line driver circuit, a clock signal (CLK) anda start pulse signal (SP) are input to the shift register, and then aselection signal is generated. The generated selection signal isbuffered and amplified in the buffer, and the resulting signal issupplied to a corresponding scan line. Gate electrodes of transistors inpixels of one line are connected to a scan line. Since the transistorsin the pixels of one line must be turned on all at once, a buffer whichcan supply a large amount of current is used.

The shift register includes first to N-th pulse output circuits 10_1 to10_N (N is a natural number of 3 or more) (see FIG. 14A). A first clocksignal CK1 from a first wiring 11, a second clock signal CK2 from asecond wiring 12, a third clock signal CK3 from a third wiring 13, and afourth clock signal CK4 from a fourth wiring 14 are supplied in thefirst to N-th pulse output circuits 10_1 to 10_N of the shift registerillustrated in FIG. 14A. In addition, a start pulse SP1 (a first startpulse) from a fifth wiring 15 is input to the first pulse output circuit10_1. Further, a signal from the pulse output circuit 10_(n−1) of theprevious stage (referred to as a previous stage signal OUT (n−1)) isinput to the n-th pulse output circuit 10_n (n is a natural number of 2or more and N or less) in a second or subsequent stage. A signal fromthe third pulse output circuit 10_3 which is two stages after the firstpulse output circuit 10_1 is input to the first pulse output circuit10_1. Similarly, a signal from the (n+2)-th pulse output circuit10_(n+2) which is two stages after the n-th pulse output circuit 10_n(referred to as a subsequent stage signal OUT (n+2)) is input to then-th pulse output circuit 10_n in the second or subsequent stage.Therefore, the pulse output circuits in respective stages output firstoutput signals (OUT (1) (SR) to OUT (N) (SR)) which is input to thepulse output circuit in the previous and/or subsequent stage, and secondoutput signals (OUT (1) to OUT (N)) which is input to other circuits andthe like. Note that as illustrated in FIG. 14A, since the subsequentstage signal OUT (n+2) is not input to the last two stages of the shiftregister, a second start pulse SP2 and a third start pulse SP3 may beseparately input to the last two stages of the shift register, forexample.

Note that a clock signal (CK) is a signal which oscillates between anH-level signal and an L-level signal (also referred to as L signal or asignal at a low power supply potential level) at regular intervals.Here, the first to fourth clock signals CK1 to CK4 are delayed by ¼cycle sequentially (i.e., they are 90° out of phase with each other). Inthis embodiment, by using the first to fourth clock signals CK1 to CK4,control or the like of driving of the pulse output circuits isperformed. The clock signal is also referred to as GCK or SCK inaccordance with a driver circuit to which the signal is input; however,here, description is made using CK as the clock signal.

FIG. 14B is one of the pulse output circuits 10_1 to 10_N shown in FIG.14A. A first input terminal 21, a second input terminal 22, and a thirdinput terminal 23 are electrically connected to any of the first tofourth wirings 11 to 14. For example, in FIG. 14A, the first inputterminal 21 of the first pulse output circuit 10_1 is electricallyconnected to the first wiring 11, the second input terminal 22 of thefirst pulse output circuit 10_1 is electrically connected to the secondwiring 12, and the third input terminal 23 of the first pulse outputcircuit 10_1 is electrically connected to the third wiring 13. Inaddition, the first input terminal 21 of the second pulse output circuit102 is electrically connected to the second wiring 12, the second inputterminal 22 of the second pulse output circuit 10_2 is electricallyconnected to the third wiring 13, and the third input terminal 23 of thesecond pulse output circuit 102 is electrically connected to the fourthwiring 14.

Each of the first to N-th pulse output circuits 10_1 to 10_N includesthe first input terminal 21, the second input terminal 22, the thirdinput terminal 23, a fourth input terminal 24, a fifth input terminal25, a first output terminal 26, and a second output terminal 27 (seeFIG. 14B). In the first pulse output circuit 10_1, the first clocksignal CK1 is input to the first input terminal 21; the second clocksignal CK2 is input to the second input terminal 22; the third clocksignal CK3 is input to the third input terminal 23; the start pulse isinput to the fourth input terminal 24; the subsequent stage signal OUT(3) is input to the fifth input terminal 25; the first output signal OUT(1) (SR) is output from the first output terminal 26; and the secondoutput signal OUT (1) is output from the second output terminal 27.

In addition to a thin film transistor (TFT) having three terminals, thethin film transistor having four terminals, which is described in theabove embodiment, can be used for each of the first to N-th pulse outputcircuits 10_1 to 10_N. Note that in this specification, when a thin filmtransistor includes two gate electrodes with a semiconductor layertherebetween, the gate electrode which is located below thesemiconductor layer is also referred to as a lower gate electrode andthe gate electrode which is located above the semiconductor layer isalso referred to as an upper gate electrode.

When an oxide semiconductor is used for a semiconductor layer includinga channel formation region of a thin film transistor, threshold voltageis shifted in a negative or positive direction in some cases dependingon a manufacturing process. Thus, a thin film transistor in which anoxide semiconductor is used for a semiconductor layer including achannel formation region preferably has a structure where thresholdvoltage can be controlled. The threshold voltage of a thin filmtransistor having four terminals can be controlled to be a desired valueby controlling a potential of an upper gate electrode and/or a lowergate electrode.

Next, an example of a specific circuit structure of the pulse outputcircuit illustrated in FIG. 14B is described with reference to FIG. 14C.

The pulse output circuit illustrated in FIG. 14C includes first tothirteenth transistors 31 to 43. In addition to the first to fifth inputterminal 21 to 25, signals or power supply potentials are supplied tothe first to thirteenth transistors 31 to 43 from a power supply line 51to which a first high power supply potential VDD is supplied, a powersupply line 52 to which a second high power supply potential VCC issupplied, and a power supply line 53 to which a low power supplypotential VSS is supplied. Signals or the like are output through thefirst output terminal 26 and the second output terminal 27. Here, thepower supply potentials of the power supply lines in FIG. 14C are set sothat the first power supply potential VDD is higher than or equal to thesecond power supply potential VCC and the second power supply potentialVCC is higher than the third power supply potential VSS. Although thefirst to fourth clock signals CK1 to CK4 are signals which oscillatebetween an H-level signal and an L-level signal at regular intervals, apotential is VDD when the clock signal is at the H level, and thepotential is VSS when the clock signal is at the L level. When thepotential VDD of the power supply line 51 is set to higher than thepotential VCC of the power supply line 52, a potential applied to thegate electrode of the transistor can be lowered without adverselyaffecting the operation, whereby the shift of the threshold voltage ofthe transistor can be reduced and deterioration can be suppressed. Notethat a thin film transistor having four terminals is preferably used forthe first transistor 31 and the sixth to ninth transistors 36 to 39among the first to thirteenth transistors 31 to 43. The first transistor31 and the sixth to ninth transistors 36 to 39 are required to switch apotential of each node connected to one of electrodes which is to be asource or a drain by a control signal of the gate electrode. The firsttransistor 31 and the sixth to ninth transistors 36 to 39 can furtherreduce malfunctions of the pulse output circuits by quick response(sharp rising of on current) with respect to a control signal input tothe gate electrode. Therefore, when a thin film transistor having fourterminals is used, the threshold voltage can be controlled andmalfunctions of the pulse output circuits can be further reduced.

In FIG. 14C, a first terminal of the first transistor 31 is electricallyconnected to the power supply line 51, a second terminal of the firsttransistor 31 is electrically connected to a first terminal of the ninthtransistor 39, and gate electrodes (a lower gate electrode and an uppergate electrode) of the first transistor 31 are electrically connected tothe fourth input terminal 24. A first terminal of the second transistor32 is electrically connected to the power supply line 53, a secondterminal of the second transistor 32 is electrically connected to thefirst terminal of the ninth transistor 39, and a gate electrode of thesecond transistor 32 is electrically connected to a gate electrode ofthe fourth transistor 34. A first terminal of the third transistor 33 iselectrically connected to the first input terminal 21, and a secondterminal of the third transistor 33 is electrically connected to thefirst output terminal 26. A first terminal of the fourth transistor 34is electrically connected to the power supply line 53, and a secondterminal of the fourth transistor 34 is electrically connected to thefirst output terminal 26. A first terminal of the fifth transistor 35 iselectrically connected to the power supply line 53, a second terminal ofthe fifth transistor 35 is electrically connected to the gate electrodeof the second transistor 32 and the gate electrode of the fourthtransistor 34, and a gate electrode of the fifth transistor 35 iselectrically connected to the fourth input terminal 24. A first terminalof the sixth transistor 36 is electrically connected to the power supplyline 52, a second terminal of the sixth transistor 36 is electricallyconnected to the gate electrode of the second transistor 32 and the gateelectrode of the fourth transistor 34, and gate electrodes (a lower gateelectrode and an upper gate electrode) of the sixth transistor 36 areelectrically connected to the fifth input terminal 25. A first terminalof the seventh transistor 37 is electrically connected to the powersupply line 52, a second terminal of the seventh transistor 37 iselectrically connected to a second terminal of the eighth transistor 38,and gate electrodes (a lower gate electrode and an upper gate electrode)of the seventh transistor 37 are electrically connected to the thirdinput terminal 23. A first terminal of the eighth transistor 38 iselectrically connected to the gate electrode of the second transistor 32and the gate electrode of the fourth transistor 34, and gate electrodes(a lower gate electrode and an upper gate electrode) of the eighthtransistor 38 is electrically connected to the second input terminal 22.The first terminal of the ninth transistor 39 is electrically connectedto the second terminal of the first transistor 31 and the secondterminal of the second transistor 32, a second terminal of the ninthtransistor 39 is electrically connected to a gate electrode of the thirdtransistor 33 and a gate electrode of the tenth transistor 40, and gateelectrodes (a lower gate electrode and an upper gate electrode) of theninth transistor 39 are electrically connected to the power supply line52. A first terminal of the tenth transistor 40 is electricallyconnected to the first input terminal 21, a second terminal of the tenthtransistor 40 is electrically connected to the second output terminal27, and the gate electrode of the tenth transistor 40 is electricallyconnected to the second terminal of the ninth transistor 39. A firstterminal of the eleventh transistor 41 is electrically connected to thepower supply line 53, a second terminal of the eleventh transistor 41 iselectrically connected to the second output terminal 27, and a gateelectrode of the eleventh transistor 41 is electrically connected to thegate electrode of the second transistor 32 and the gate electrode of thefourth transistor 34. A first terminal of the twelfth transistor 42 iselectrically connected to the power supply line 53, a second terminal ofthe twelfth transistor 42 is electrically connected to the second outputterminal 27, and a gate electrode of the twelfth transistor 42 iselectrically connected to the gate electrodes (the lower gate electrodeand the upper gate electrode) of the seventh transistor 37. A firstterminal of the thirteenth transistor 43 is electrically connected tothe power supply line 53, a second terminal of the thirteenth transistor43 is electrically connected to the first output terminal 26, and a gateelectrode of the thirteenth transistor 43 is electrically connected tothe gate electrodes (the lower gate electrode and the upper gateelectrode) of the seventh transistor 37.

In FIG. 14C, a connection point of the gate electrode of the thirdtransistor 33, the gate electrode of the tenth transistor 40, and thesecond terminal of the ninth transistor 39 is referred to as a node A.In addition, a connection point of the gate electrode of the secondtransistor 32, the gate electrode of the fourth transistor 34, thesecond terminal of the fifth transistor 35, the second terminal of thesixth transistor 36, the first terminal of the eighth transistor 38, andthe gate electrode of the eleventh transistor 41 is referred to as anode B.

FIG. 15A illustrates signals input to the first to fifth input terminals21 to 25 and signals output from the first output terminal 26 and thesecond output terminal 27 when the pulse output circuit illustrated inFIG. 14C is used as the first pulse output circuit 10_1.

Specifically, the first clock signal CK1 is input to the first inputterminal 21; the second clock signal CK2 is input to the second inputterminal 22; the third clock signal CK3 is input to the third inputterminal 23; the start pulse (SP1) is input to the fourth input terminal24; the subsequent stage signal OUT (3) is input to the fifth inputterminal 25; the first output signal OUT (1) (SR) is output from thefirst output terminal 26; and the second output signal OUT (1) is outputfrom the second output terminal 27.

Note that a thin film transistor is an element having at least threeterminals of a gate, a drain, and a source. Further, the thin filmtransistor includes a semiconductor in which a channel region is formedin a region overlapping with the gate and the amount of current whichflows between the drain and the source through the channel region can becontrolled by controlling a potential of the gate. Here, since thesource and the drain of the thin film transistor may change depending onthe structure, the operating condition, and the like of the thin filmtransistor, it is difficult to define which is a source or a drain.Therefore, a region functioning as a source or a drain is not called asource or a drain in some cases. In such a case, for example, one of thesource and the drain may be referred to as a first terminal and theother thereof may be referred to as a second terminal.

Note that in FIG. 14C and FIG. 15A, a capacitor for performing bootstrapoperation by setting the node A floating may be additionally provided.Further, a capacitor having one electrode electrically connected to thenode B may be additionally provided in order to hold a potential of thenode B.

Here, FIG. 15B illustrates a timing chart of a shift register includinga plurality of the pulse output circuits illustrated in FIG. 15A. Notethat in the case where the shift register is a scan line driver circuit,a period 61 of FIG. 15B corresponds to a vertical retrace period and aperiod 62 of FIG. 15B corresponds to a gate selection period.

Note that as illustrated in FIG. 15A, with the ninth transistor 39 whosegate is supplied with the second power supply potential VCC, advantagesdescribed below are obtained before and after bootstrap operation.

Without the ninth transistor 39 whose gate is supplied with the secondpower supply potential VCC, when a potential of the node A is raised bybootstrap operation, a potential of a source which is the secondterminal of the first thin film transistor 31 increases to a valuehigher than the first power supply potential VDD. Then, the firstterminal of the first transistor 31, that is, the terminal on the powersupply line 51 side, comes to serve as a source of the first transistor31. Therefore, in the first transistor 31, a high bias voltage isapplied and thus significant stress is applied between the gate and thesource and between the gate and the drain, which might causedeterioration in the transistor. Thus, with the ninth transistor 39whose gate electrode is supplied with the second power supply potentialVCC, the potential of the node A is raised by bootstrap operation, butat the same time, an increase in the potential of the second terminal ofthe first transistor 31 can be prevented. In other words, with the ninthtransistor 39, the level of a negative bias voltage applied between thegate and the source of the first transistor 31 can be lowered.Accordingly, with a circuit structure in this embodiment, a negativebias voltage applied between the gate and the source of the firsttransistor 31 can be lowered, so that deterioration in the firsttransistor 31, which is due to stress, can be further restrained.

Note that the ninth transistor 39 is provided so that the first terminaland the second terminal of the ninth transistor 39 are connected betweenthe second terminal of the first transistor 31 and the gate of the thirdtransistor 33. In the case where a shift register includes a pluralityof pulse output circuits of this embodiment, the ninth transistor 39 maybe eliminated in a signal line driver circuit which has more stages thana scan line driver circuit, which is advantageous in reducing the numberof the transistors.

When an oxide semiconductor is used for each of the semiconductor layersof the first to thirteenth transistors 31 to 43, the amount of offcurrent of the thin film transistors can be reduced, the amount of oncurrent and field-effect mobility can be increased, and, the rate ofdeterioration can be decreased, whereby malfunctions of the circuit canbe reduced. Further, a transistor including an oxide semiconductor has alower rate of deterioration of the transistor due to application of ahigh potential to a gate electrode, as compared to a transistorincluding amorphous silicon. Therefore, even when the first power supplypotential VDD is supplied to the power supply line to which the secondpower supply potential VCC is supplied, similar operation can beperformed and the number of power supply lines provided between thecircuits can be reduced, whereby size reduction in a circuit can beachieved.

Note that a similar effect is obtained even when a connection relationis changed so that a clock signal which is supplied to the gateelectrodes (the lower gate electrode and the upper gate electrode) ofthe seventh transistor 37 through the third input terminal 23 is a clocksignal which is supplied to the gate electrodes (the lower gateelectrode and the upper electrode) of the seventh transistor 37 throughthe second input terminal 22; and a clock signal which is supplied tothe gate electrodes (the lower gate electrode and the upper gateelectrode) of the eighth transistor 38 through the second input terminal22 is a clock signal which is supplied to the gate electrodes (the lowerelectrode and the upper electrode) of the eighth transistor 38 throughthe third input terminal 23. Note that in the shift register illustratedin FIG. 15A, the seventh transistor 37 and the eighth transistor 38 areboth on, the seventh transistor 37 is turned off and the eighthtransistor 38 is kept on, and then the seventh transistor 37 kept offstate and the eighth transistor 38 is turned off, whereby the decreasein the potential of the node B, which is caused by the decrease in thepotentials of the second input terminal 22 and the third input terminal23, occurs twice due to the decrease in the potential of the gateelectrode of the seventh transistor 37 and the decrease in the potentialof the gate electrode of the eighth transistor 38. On the other hand, inthe shift register illustrated in FIG. 15A, the seventh transistor 37and the eighth transistor 38 are both on, the seventh transistor 37 iskept on and the eighth transistor 38 is turned off, and then the seventhtransistor 37 is turned off and the eighth transistor 38 is kept off,whereby the decrease in the potential of the node B, which is caused bythe decrease in the potentials of the second input terminal 22 and thethird input terminal 23, can be reduced to once due to the decrease inthe potential of the gate electrode of the eighth transistor 38 isdecreased. Accordingly, the connection relation, in which the clocksignal CK3 is supplied to the gate electrodes (the lower electrode andthe upper electrode) of the seventh transistor 37 through the thirdinput terminal 23 and the clock signal CK2 is supplied to the gateelectrodes (the lower gate electrode and the upper gate electrode) ofthe eighth transistor 38 through the second input terminal 22, ispreferable. That is because the number of times of fluctuation of thepotential of the node B can be reduced and noise can be reduced.

In this way, in a period during which the potential of the first outputterminal 26 and the potential of the second output terminal 27 are heldat the L level, an H level signal is regularly supplied to the node B;therefore, a malfunction of the pulse output circuit can be suppressed.

This embodiment can be implemented in appropriate combination with thestructures described in the other embodiments.

(Embodiment 10)

A light-emitting device disclosed in this specification can be appliedto a variety of electronic devices (including an amusement machine).Examples of electronic devices are a television set (also referred to asa television or a television receiver), a monitor of a computer or thelike, a camera such as a digital camera or a digital video camera, adigital photo frame, a mobile phone (also referred to as a cellularphone or a mobile phone device), a portable game console, a portableinformation terminal, an audio reproducing device, a large-sized gamemachine such as a pachinko machine, and the like.

FIG. 23A illustrates a mobile phone 1100. The mobile phone 1100 isprovided with a display portion 1102 incorporated in a housing 1101,operation buttons 1103, an external connection port 1104, a speaker1105, a microphone 1106, and the like.

When the display portion 1102 illustrated in FIG. 23A is touched with afinger or the like, data can be input into the mobile phone 1100.Further, operations such as making a call and texting can be performedby touching the display portion 1102 with a finger or the like.

There are mainly three screen modes of the display portion 1102. Thefirst mode is a display mode mainly for displaying images. The secondmode is an input mode mainly for inputting data such as text. The thirdmode is a display-and-input mode in which two modes of the display modeand the input mode are combined.

For example, in the case of making a call or texting, the input modemainly for inputting text is selected for the display portion 1102 sothat characters displayed on a screen can be input. In this case, it ispreferable to display a keyboard or number buttons on almost the entirescreen of the display portion 1102.

When a detection device including a sensor for detecting inclination,such as a gyroscope or an acceleration sensor, is provided inside themobile phone 1100, display on the screen of the display portion 1102 canbe automatically switched by determining the direction of the mobilephone 1100 (whether the mobile phone 1100 is placed horizontally orvertically for a landscape mode or a portrait mode).

The screen mode is switched by touching the display portion 1102 oroperating the operation buttons 1103 of the housing 1101. Alternatively,the screen modes may be switched depending on the kind of the imagedisplayed on the display portion 1102. For example, when a signal of animage displayed on the display portion is a signal of moving image data,the screen mode is switched to the display mode. When the signal is asignal of text data, the screen mode is switched to the input mode.

Further, in the input mode, when input by touching the display portion1102 is not performed for a certain period while a signal detected by anoptical sensor in the display portion 1102 is detected, the screen modemay be controlled so as to be changed from the input mode to the displaymode.

The display portion 1102 may function as an image sensor. For example,an image of a palm print, a fingerprint, or the like is taken when thedisplay portion 1102 is touched with a palm or a finger, wherebypersonal identification can be performed. Further, by providing abacklight or a sensing light source which emits a near-infrared light inthe display portion, an image of a finger vein, a palm vein, or the likecan also be taken.

The light-emitting device described in any of Embodiments 1 to 9 is usedfor the display portion 1102, whereby reliability can be increased.

FIG. 23B illustrates an example of a portable information terminal Aportable information terminal whose example is illustrated in FIG. 23Bcan have a plurality of functions. For example, in addition to atelephone function, such a portable information terminal can have afunction of processing a variety of pieces of data by incorporating acomputer.

The portable information terminal illustrated in FIG. 23B has a housing1800 and a housing 1801. The housing 1801 includes a display panel 1802,a speaker 1803, a microphone 1804, a pointing device 1806, a camera lens1807, an external connection terminal 1808, and the like. The housing1800 includes a keyboard 1810, an external memory slot 1811, and thelike. In addition, an antenna is incorporated in the housing 1800 or1801.

The display panel 1802 is provided with a touch panel. A plurality ofoperation keys 1805 which is displayed as images is illustrated bydashed lines in FIG. 23B.

Further, in addition to the above structure, a contactless IC chip, asmall-sized memory device, or the like may be incorporated.

The light-emitting device of the present invention can be used for thedisplay panel 1802 and the direction of display is changed asappropriate depending on an application mode. Further, the camera lens1807 is provided on the same surface as the display panel 1802, and thusit can be used as a video phone. The speaker 1803 and the microphone1804 can be used for videophone calls, recording, and playing sound,etc. as well as voice calls. Moreover, the housings 1800 and 1801 in astate where they are developed as illustrated in FIG. 23B can be slid sothat one is lapped over the other; therefore, the size of the portableinformation terminal can be reduced, which makes the portableinformation terminal suitable for being carried.

The external connection terminal 1808 can be connected to an AC adapterand various types of cables such as a USB cable, and charging and datacommunication with a personal computer are possible. Moreover, a storagemedium can be inserted into the external memory slot 1811 so that alarge amount of data can be stored and can be moved.

Further, in addition to the above functions, an infrared communicationfunction, a television reception function, or the like may be provided.

FIG. 24A illustrates a television set 9600. In the television set 9600,a display portion 9603 is incorporated in a housing 9601. The displayportion 9603 can display images. Here, the housing 9601 is supported bya stand 9605.

The television set 9600 can be operated with an operation switch of thehousing 9601 or a separate remote controller 9610. Channels and volumecan be controlled with an operation key 9609 of the remote controller9610, so that an image displayed on the display portion 9603 can becontrolled. Furthermore, the remote controller 9610 may be provided witha display portion 9607 for displaying data output from the remotecontroller 9610.

Note that the television set 9600 is provided with a receiver, a modem,and the like. With the use of the receiver, general televisionbroadcasting can be received. Moreover, when the display device isconnected to a communication network with or without wires via themodem, one-way (from a sender to a receiver) or two-way (between asender and a receiver or between receivers) information communicationcan be performed.

The light-emitting device described in any of Embodiments 1 to 9 is usedfor the display portion 9603, whereby reliability can be increased.

FIG. 24B illustrates a digital photo frame 9700. For example, in thedigital photo frame 9700, a display portion 9703 is incorporated in ahousing 9701. The display portion 9703 can display a variety of images.For example, the display portion 9703 can display data of an image takenwith a digital camera or the like and function as a normal photo frame.

The light-emitting device described in any of Embodiments 1 to 9 is usedfor the display portion 9703, whereby reliability can be increased.

Note that the digital photo frame 9700 is provided with an operationportion, an external connection terminal (a USB terminal, a terminalthat can be connected to various cables such as a USB cable, or thelike), a recording medium insertion portion, and the like. Althoughthese components may be provided on the surface on which the displayportion is provided, it is preferable to provide them on the sidesurface or the back surface for the design of the digital photo frame9700. For example, a memory storing data of an image taken with adigital camera is inserted in the recording medium insertion portion ofthe digital photo frame, whereby the image data can be transferred andthen displayed on the display portion 9703.

The digital photo frame 9700 may be configured to transmit and receivedata wirelessly. The structure may be employed in which desired imagedata is transferred wirelessly to be displayed.

FIG. 25 is a portable game machine and is constituted by two housings ofa housing 9881 and a housing 9891 which are connected with a jointportion 9893 so that the portable game machine can be opened or folded.A display portion 9882 and a display portion 9883 are incorporated inthe housing 9881 and the housing 9891, respectively.

The light-emitting device described in any of Embodiments 1 to 9 is usedfor the display portions 9882 and 9883, whereby reliability can beincreased.

The portable game machine illustrated in FIG. 25 is provided with aspeaker portion 9884, a recording medium insertion portion 9886, an LEDlamp 9890, input means (operation keys 9885, a connection terminal 9887,a sensor 9888 (having a function of measuring force, displacement,position, speed, acceleration, angular velocity, rotation number,distance, light, liquid, magnetism, temperature, chemical substance,sound, time, hardness, electric field, current, voltage, electric power,radial ray, flow rate, humidity, gradient, vibration, smell, or infraredray), and a microphone 9889), and the like. Needless to say, thestructure of the portable game machine is not limited to the above andother structures provided with at least a thin film transistor disclosedin this specification can be employed. The portable game machine mayinclude an additional accessory as appropriate. The portable gamemachine illustrated in FIG. 25 has a function of reading a program ordata stored in the recording medium to display it on the displayportion, and a function of sharing data with another portable gamemachine by wireless communication. Note that a function of the portablegame machine illustrated in FIG. 25 is not limited to those describedabove, and the portable game machine can have a variety of functions.

FIG. 26 is an example in which the light-emitting device formed inaccordance with the above embodiments is used as an indoor lightingdevice 3001. Since the light-emitting device described in the aboveembodiments can be increased in area, the light-emitting device can beused as a lighting device having a large area. Further, thelight-emitting device described in Embodiment 2 can be used as a desklamp 3000. Note that the lighting equipment includes, in its category, aceiling light, a wall light, a lightning for an inside of a car, anemergency exit light, and the like.

As described above, the light-emitting device described in any ofEmbodiments 1 to 9 can be used in the display panels of a variety ofelectronic devices such as the above ones, and thus an electronic devicewith high reliability can be provided.

This application is based on Japanese Patent Application serial no.2009-204972 filed with Japan Patent Office on Sep. 4, 2009, the entirecontents of which are hereby incorporated by reference.

EXPLANATION OF REFERENCE

-   10: pulse output circuit, 11: wiring, 12: wiring, 13: wiring, 14:    wiring, 15: wiring, 21: input terminal, 1 22: input terminal, 23:    input terminal. 24: input terminal. 25: input terminal, 26: output    terminal. 27: output terminal, 31: transistor, 32: transistor, 33:    transistor, 34: transistor, 35: transistor, 36: transistor, 37:    transistor, 38: transistor, 39: transistor, 40: transistor. 41:    transistor, 42: transistor. 43: transistor, 51: power supply line,    52: power supply line, 53: power supply line, 100: substrate, 101:    gate electrode layer, 102: gate insulating layer, 103: oxide    semiconductor layer. 106: protective insulating layer, 107: oxide    insulating film, 108: capacitor wiring layer, 109: protective    insulating layer, 110: electrode layer, 111: conductive layer, 112:    conductive layer, 113: terminal electrode, 116: channel formation    region, 118: contact hole, 119: contact hole, 120: connection    electrode, 121: terminal, 122: terminal, 125: contact hole, 126:    contact hole, 127: contact hole, 128: terminal electrode, 129:    terminal electrode, 130: oxide semiconductor film, 131: oxide    semiconductor layer. 133: oxide semiconductor layer, 134: oxide    semiconductor layer. 137: resist mask, 138: oxide conductive layer,    140: oxide conductive film, 142: oxide conductive layer. 143: oxide    conductive layer. 145: wiring layer, 146: capacitor, 147: capacitor.    149: capacitor electrode layer, 150: terminal, 151: terminal, 153:    connection electrode, 155: conductive film, 156: electrode. 161:    gate electrode layer, 162: conductive layer. 163: oxide    semiconductor layer, 166: channel formation region, 168: oxide    semiconductor layer, 170: thin film transistor, 171: thin film    transistor, 172: thin film transistor, 173: thin film transistor.    180: thin film transistor, 181: thin film transistor, 182: thin film    transistor, 183: thin film transistor, 185: capacitor electrode    layer, 191: color filter layer, 192: overcoat layer, 193: partition.    194: EL layer, 195: electrode layer. 196: connection electrode    layer, 198: oxide semiconductor layer. 1001: electrode, 1002:    electrode, 1003: EL layer, 1004: charge generation layer, 104 a:    oxide conductive layer, 104 b: oxide conductive layer, 105a: source    electrode layer, 105 b: drain electrode layer, 1100: mobile phone,    1101: housing, 1102: display portion, 1103: operation button, 1104:    external connection port, 1105: speaker, 1106: microphone, 117 a:    high-resistance source region. 117 b: high-resistance drain region,    135 a: resist mask, 136 a: resist mask, 164 a: oxide conductive    layer, 164 b: oxide conductive layer. 165 a: source electrode layer,    165 b: drain electrode layer, 167 a: high-resistance source region,    167 b: high-resistance drain region, 1800: housing, 1801: housing,    1802: display panel, 1803: speaker, 1804: microphone, 1805:    operation key, 1806: pointing device, 1807: camera lens, 1808:    external connection terminal, 1810: keyboard, 1811: external memory    slot, 3000: table light, 3001: lighting device, 4501: substrate.    4502: pixel portion, 4505: sealant, 4506: substrate, 4507: filler,    4509: thin film transistor, 4510: thin film transistor, 4511:    light-emitting element, 4512: electroluminescent layer, 4513:    electrode layer, 4515: connection terminal electrode, 4516: terminal    electrode, 4517: electrode layer, 4519: anisotropic conductive film,    4520: partition, 4540: conductive layer, 4542: oxide insulating    layer, 4543: overcoat layer, 4544: insulating layer, 4545: color    filter layer, 4546: insulating layer, 5300: substrate, 5301: pixel    portion. 5302: scan line driver circuit, 5303: scan line driver    circuit, 5304: signal line driver circuit. 5305: timing control    circuit, 5601: shift register 5602: switching circuit, 5603: thin    film transistor, 5604: wiring. 5605: wiring, 6400: pixel. 6401:    switching transistor, 6402: transistor, 6403: capacitor, 6404:    light-emitting element, 6405: signal line, 6406: scan line. 6407:    power supply line, 6408: common electrode. 7001: TFT, 7002:    light-emitting element, 7003: electrode layer, 7004: EL layer, 7005:    electrode layer, 7009: partition, 7011: driver TFT, 7012:    light-emitting element, 7013: electrode layer, 7014: EL layer, 7015:    electrode layer, 7016: light-blocking film. 7017: conductive film,    7019: partition, 7021: driver TFT, 7022: light-emitting element,    7023: electrode layer, 7024: EL layer, 7025: electrode layer, 7026:    electrode layer. 7027: conductive film, 7029: partition. 7031: oxide    insulating layer, 7032: protective insulating layer, 7033: color    filter layer, 7034: overcoat layer, 7035: protective insulating    layer, 7041: oxide insulating layer, 7042: protective insulating    layer, 7043: color filter layer, 7044: overcoat layer, 7045:    protective insulating layer, 7051: oxide insulating layer, 7052:    protective insulating layer, 7053: planarizing insulating layer,    7055: protective insulating layer, 9600: television device, 9601:    housing, 9603: display portion. 9605: stand. 9607: display portion,    9609: operation key, 9610: remote controller, 9700: digital photo    frame, 9701: housing, 9703: display portion, 9881: housing, 9882:    display portion, 9883: display portion, 9884: speaker portion, 9885:    operation key. 9886: recording media insertion portion, 9887:    connection terminal, 9888: sensor, 9889: microphone, 9890: LED lamp,    9891: housing, 4503 a: signal line driver circuit, and 4504 a: scan    line driver circuit.

The invention claimed is:
 1. A light emitting device comprising: asubstrate; a transistor comprising: a first conductive layer over thesubstrate; a first oxide insulating layer over the first conductivelayer; an oxide semiconductor layer over the first oxide insulatinglayer; a second oxide insulating layer over the oxide semiconductorlayer; and a second conductive layer and a third conductive layerelectrically connected to the oxide semiconductor layer; a firstinsulating layer over the second and third conductive layers, the firstinsulating layer comprising a contact hole; a color filter layer overthe first insulating layer; a second insulating layer over the colorfilter layer; a partition over the second insulating layer; and a pixelelectrode electrically connected to one of the second and thirdconductive layers through the contact hole, wherein the pixel electrodecomprises a depression portion overlapping with the contact hole,wherein the depression portion and the partition overlap each otherwithout the second insulating layer interposed between the depressionportion and the partition, wherein an end portion of the secondinsulating layer does not overlap with the contact hole, wherein theoxide semiconductor layer comprises a channel formation region, a firstregion, and a second region, wherein the first region and the secondregion are in contact with the second conductive layer and the thirdconductive layer, respectively, wherein the first region has resistancelower than resistance of the channel formation region, wherein thesecond region has resistance lower than resistance of the channelformation region, wherein each of the first conductive layer, the secondconductive layer, and the third conductive layer contains titanium,wherein the second insulating layer is configured to reduce roughness ofthe color filter layer, and wherein the color filter layer does notoverlap with the channel formation region.
 2. The light emitting deviceaccording to claim 1, wherein the oxide semiconductor layer comprisesindium, gallium, and zinc.
 3. The light emitting device according toclaim 1, wherein the oxide semiconductor layer comprises indium, tin,and zinc.
 4. The light emitting device according to claim 1, wherein theoxide semiconductor layer comprises a region being in an oxygen-excessstate.
 5. The light emitting device according to claim 1, wherein eachof the first conductive layer, the second conductive layer, and thethird conductive layer further contains molybdenum.
 6. The lightemitting device according to claim 1, wherein each of the secondconductive layer and the third conductive layer is configured to asource electrode or a drain electrode.
 7. The light emitting deviceaccording to claim 1, wherein emission color of a light emitting elementcomprising the pixel electrode is white.
 8. The light emitting deviceaccording to claim 1, wherein a light emitting element comprising thepixel electrode comprises a first light emitting unit and a second lightemitting unit, and wherein a charge generation layer is provided betweenthe first light emitting unit and the second light emitting unit.
 9. Thelight emitting device according to claim 1, wherein a light emittingelement comprising the pixel electrode comprises a first light emittingunit and a second light emitting unit, wherein emission color of thefirst light emitting unit is blue, and wherein emission color of thesecond light emitting unit is yellow.
 10. The light emitting deviceaccording to claim 1, wherein each of the color filter layer and a lightemitting element comprising the pixel electrode is included in a displayportion.
 11. A light emitting device comprising: a pixel portioncomprising: a first transistor comprising a first oxide semiconductorlayer; a first protective layer over the first transistor, the firstprotective layer comprising a contact hole; a color filter layer overthe first protective layer; a second protective layer over the colorfilter layer; an insulating layer over the second protective layer; apartition of the insulating layer; and a pixel electrode electricallyconnected to the first transistor through the contact hole; and acircuit portion comprising: a second transistor comprising a secondoxide semiconductor layer, wherein the pixel electrode comprises adepression portion overlapping with the contact hole, wherein thedepression portion and the partition overlap each other without theinsulating layer interposed between the depression portion and thepartition, wherein an end portion of the insulating layer does notoverlap with the contact hole, wherein the first oxide semiconductorlayer comprises a first channel formation region, a first region, and asecond region, wherein the first region and the second region are incontact with a first source electrode of the first transistor and afirst drain electrode of the first transistor, respectively, wherein thefirst region has resistance lower than resistance of the first channelformation region, wherein the second region has resistance lower thanresistance of the first channel formation region, wherein the secondoxide semiconductor layer comprises a second channel formation region, athird region, and a fourth region, wherein the third region and thefourth region are in contact with a second source electrode of thesecond transistor and a second drain electrode of the second transistor,respectively, wherein the third region has resistance lower thanresistance of the second channel formation region, wherein the fourthregion has resistance lower than resistance of the second channelformation region, and wherein the color filter layer does not overlapwith the first channel formation region.
 12. The light emitting deviceaccording to claim 11, wherein the first and second oxide semiconductorlayers comprise indium, gallium, and zinc.
 13. The light emitting deviceaccording to claim 11, wherein the first and second oxide semiconductorlayers comprise indium, tin, and zinc.
 14. The light emitting deviceaccording to claim 11, wherein the first and second oxide semiconductorlayers comprise a region being in an oxygen-excess state.
 15. The lightemitting device according to claim 11, wherein each of the first source,first drain, second source, and second drain electrodes containstitanium.
 16. The light emitting device according to claim 15, whereineach of the first source, first drain, second source, and second drainelectrodes further contains molybdenum.
 17. The light emitting deviceaccording to claim 11, wherein emission color of a light emittingelement comprising the pixel electrode is white.
 18. The light emittingdevice according to claim 11, wherein a light emitting elementcomprising the pixel electrode comprises a first light emitting unit anda second light emitting unit, and wherein a charge generation layer isprovided between the first light emitting unit and the second lightemitting unit.
 19. The light emitting device according to claim 11,wherein a light emitting element comprising the pixel electrodecomprises a first light emitting unit and a second light emitting unit,wherein emission color of the first light emitting unit is blue, andwherein emission color of the second light emitting unit is yellow. 20.The light emitting device according to claim 11, wherein each of thecolor filter layer and a light emitting element comprising the pixelelectrode is included in a display portion.